A ball is thrown upwards and it's height h m, at time t s, is given by h=7t-4.9t2. How long does the ball spend more than 1.5m above ground?

Answer: From what you wrote the I think the ball is drop

At time 0 you are 7 meters above ground

You basically just need to solve for

1.5 = 7t-4.9t^2

by rearrange the equation you get

4.9t^2-7t+1.5=0

by using Quadratic Formula

t=1.166s