a: 45.9 meters
b: 4.29 seconds
step-by-step explanation:
a: h(t)=1/2(-9.8)(3)^2+0(3)+90
h(t)=-4.9(3)^2+90
h(t)=-44.1+90
h(t)=45.9 meters
b: 0=1/2(-9.8)(t^2)+0t+90
0=-4.9t^2+90
-90=-4.9t^2
18.37=t^2
t=4.29 seconds
in the second question, the numbers aren't exact, but they're a close approximation.