hi, need help

A window washer drops a squeegee from a scaffold 100 m off the ground. The

relationship between the height of the squeegee (h), in metres, and the length of time

it has been falling (t), in seconds, is given by h = 100 − 5t2.

a) When does the squeegee pass a window 30 m off the ground?

b) How long does it take for the squeegee to hit the ground?

thanks!