Calc
posted by Joe .
A rock is thrown upwards (vertically) from the ground with an initial velocity of 40 feet per second. If acceleration due to gravity is 10 feet per second squared, how high will the rock go?

You are using the wrong units, the value of 10 is associated with metres not feet. (actually in most cases it is considered 9.8 )
I will assume you meant metres, not feet
height = 5t^2 + 40t
velocity = 10t + 40
at max height, velocity = 0
10t+40 = 0
t= 4
height = 5(4^2) + 40(4) = 40 m
If your problem stated feet, then the equation would have been
height = 16t^2 + 40t
etc