6x+21+15-2x
4x+36
hope this helps...
Step-by-step explanation:
A ball is launched straight up in the air from a height of 6 feet. The velocity as a function of time t is given by :
f(t) = -32 t+285
Height of the ball is :

C is constant. Here the ball is launched from a height of 6 feet. So,

At t = 2 s, 
At t = 9 s, 
Between 2 s and 9 s, the ball's height changed is : 1275 - 512 = 763 m.