I need help plzz

Question

Lin and Clare were standing in the woods near a stream, and each threw a stone up in the air at the same time so that it would land in the water. The graph represents the height of a stone  seconds after it was tossed up by Lin.  

The function  given by  represents the height of a stone  seconds after it was thrown by Clare. In both functions, height is measured in feet.

What was the maximum height of Clare's stone?

Answer 1

f(t) = -16t^2 + 8t + 8 take the derivative and set = 0, solve for t, then substitute that value into f(t)

f'(t) = -32t + 8 = 0

t = 8/32 = 1/4 second for max height

f(1/4) = -16(1/4)^2 + 8(1/4) + 8 = -1+2 + 8 = 9 feet