Susan wants to play softball and work after school. she cannot do both, so she decides to play softball. what is her opportunity cost? a. playing softball b. working c. being with her friends d. there is no opportunity cost because she spends no money.

For positive constants a and b, the force between two atoms in a molecule is given f(r) = −a r2 + b r3 , where r > 0 is the distance between the atoms. note: a and b are upper case letters. (a) find f '(r) = (b) find the critical point for f(r). r = (c) find f ''(r) = (d) find the value of r so that f ''(r) = 0.