### Home > PC > Chapter 5 > Lesson 5.2.1 > Problem 5-53

5-53.

Do not forget the constant of proportionality (*k*).

*S*(*r*) = *kr*^{2}

Substitute the given point (*r*,*S*) into your function in part (a) to find *k*.

Then use the resulting equation to find the surface area when *r* = 3 cm.