Dear student,

Please you have to check once again your question, because according to me in place "r" it should be "t".

So, I am solving question by taking the question as - A=3t^2 + t/5+7

Now rate of anything wrt time is : d(anything) / dt.

Therefore the rate of area wrt time is = d(A) / dt
d(A) / dt = 6t +1/5 + 0 = 6t + 1/5.

Now therefore the rate of change (increase) of area wrr time in 5 seconds will be :-

d(A) / dt (at t = 5) = 30 + 1/5 = 151/5 = 30.2