2a. A(t) = π(70 + 6t)^2 (Let t = 2 hours)
A(2) = π(70 + 6(2))^2 = 6724π
Now let t = 0 hours (result from part 1)
A(t) = π(70 + 6(0))^2 = 4900π
Average rate = 6724π - 4900π/2-0 = 912π
912π area covered per hour
2b. Let t = 1/2 hours, A(t) = π(70 + 6(1/2))^2 = 5329π,
Let t = 0 hours - result from last time was 4900π,
Average rate = 5329π - 4900π/1/2 - 0 = 858π
858π area covered per hour