Stuck on math problem

Question

The radius of the circular top or bottom of a tin can with a surface area S and a height h is given by r = (- h + sqrt(h ^ 2 + 0.64S))/2 What radius should be used to make a can with a height of 15 in and a surface area of 2025 in²?

Answer 1

r= (-h + sqr(h^2 + .64S)/2

r = (-15 + sqr((-15)^2 + .64(2025))/2

= (-15+ sqr(225 + 1296)/2

= (-15 + sqr(1521)/2

= (-15 + 39)/2

= 24/2

= 12 inches = radius

Surface Area = S= 2pir^2 +pi(2r)h

= 2pi(12)^2 + pi(24)15

= pi(288 +360)

= 648pi

= about 648(3.14)

= about 2035