the formula for volume of a cylinder is : V = PI x r^2 x H
for both questions, plug in the known information and solve for the unknown:
Q1) V = 450, H = 8
so 450 = 3.14 x r^2 x 8
450 = r^2 x 25.12
r^2 = 450 / 25.12 = 17.914
r = sqrt(17.914) = 4.23 rounded to nearest tenth = 4.2 inches
Q2) V = 500, r=6
500 = 3.14 x 6^2 x H
500 = 3.14 x 36 x h
500 = 113.04 x h
h = 500 / 113.047 = 4.42 = 4.4 inches