Combine related tasks into one activity in AD3 (#122)

* Combine related tasks into one activity in AD3

* Update 03.ptx

---------

Co-authored-by: Steven Clontz <steven.clontz@gmail.com>

Author: siwelwerd

source/03-AD/03.ptx

@@ -279,30 +279,42 @@ recall that when <m>y</m> is a function of <m>x</m>, which in turn is a function
 
 <!-- Using triangles     -->
 
-<remark xml:id="right-triangles-sides-theorem">
+<activity xml:id="right-triangles-related-rates">
+  <introduction>
 <p>Recall that in a right triangle with sides <m>a,b</m> and hypotenuse <m>c</m> we have the relationship </p>
 <me> a^2 + b^2 = c^2,</me>
 <p>also known in the western world as the Pythagorean theorem (even though this result was well know well before his time by other civilizations).</p> 
-    </remark>
+  </introduction>
 
-<activity xml:id="right-triangles-related-rates"><p> Notice that by differentiating each variable in the equation above with respect to <m>t</m>, we get a relationship between <m>\frac{da}{dt}, \frac{db}{dt}, \frac{dc}{dt}</m>. Find this related rates equation!    </p></activity>    
+<task>
+  <statement>
+    <p> Notice that by differentiating the equation above with respect to <m>t</m> we get a relationship between
+      <m>a,b,c, \frac{da}{dt}, \frac{db}{dt}, \frac{dc}{dt}</m>. Find this related rates equation.    
+    </p>
+  </statement>
+</task>
 
-
-<activity xml:id="rel-rates-right-triangles1">
-   <p> A rectangle has one side of 8 cm. How fast is the diagonal of the rectangle changing at the instant when the other side is 6 cm and increasing at a rate of 3 cm per minute?
+<task>
+  <statement>
+   <p> A rectangle has one side of 8 cm. How fast is the diagonal of the rectangle changing at the instant when the other 
+    side is 6 cm and increasing at a rate of 3 cm per minute?
  </p>  
-   </activity>
-
+</statement>
+</task>
 
-<activity xml:id="rel-rates-right-triangles2">
-   <p> A 10 m ladder leans against a vertical wall and the bottom of the ladder slides away at a rate of 0.5 m/sec. When is the top of the ladder sliding the fastest down the wall?
+<task>
+  <statement>
+   <p> A 10 m ladder leans against a vertical wall and the bottom of the ladder slides away at a rate of 0.5 m/sec. 
+    When is the top of the ladder sliding the fastest down the wall?
  </p> 
      <ol marker="A." cols="2">
                 <li><p>  When the bottom of the ladder is 4 meters from the wall. </p></li>
                   <li><p> When the bottom of the ladder is 8 meters from the wall. </p></li> 
                   <li><p> The top of the ladder is sliding down at a constant rate. </p></li>   
-              </ol>      
-   </activity>
+      </ol>      
+  </statement>
+</task>
+</activity>
 
 <activity xml:id="related-rates_fluency-checkit">