8. volume of cylinder is pi*r^2*h So V= pi * (radius)^2 * height =720* pi
we know circumference = 2 * pi * r
if we look at first equation. We can edit it like pi * r * r * h
now we can say it kind of looks like circumference equation but missing 2 so we multiply both sides by 2 2 * pi * r * r * h = 2 * 720 * pi
We can take out the 2 * pi * r and put in circumference (C)
c * r * h = 1440 * pi
We we know h is 20 so
c * r * 20 = 1440 * pi c * r = 72 * pi
we have to solve for r first so break circumference back up
2 * pi * r * r = 72 * pi
r * r = 36 r = 6
plug into circum equation C = 2 * pi * 6 C = 12 * pi
10. I assume the cylinders fill uo the box and if radius is 1.5 then diameter is 3. There are 5 in a row some 3 * 5 = 15 box length. 2 in a column so 2 * 3 = 6 box width the height is 5
