Answer:
A' = 6(3t +1)
Step-by-step explanation:
The area is the square of the side length, so ...
A = (3t +1)²
The derivative with respect to t is then
A' = 2(3t +1)·(3) = 6(3t +1)
If you like, you can multiply out the area expression first, then differentiate.
A = 9t² +6t +1
A' = 18t +6
This can be factored, if you like, to ...
A' = 6(3t +1)
