The height of a soccer ball after it is kicked into the air is given by h(t)=-4.9t^2+3.5t+1, where h is the height in metres and t is the time in seconds

a)determine the rate of change of the height of the soccer ball at time t.

-9.8x+3.5 didnt have problem with that

b) Determine the rate of change of the height of the soccer ball at 0.5s

-9.8(0.5)+3.5= -1.4m/s no problem with that

c) When does the ball momentarily stop?

What is the height of the ball at this time?

...... have no clue......