Prime Factors of 60: 2,3, and 5
Prime Factors of 140: 2,5 and 7
All mental math no work needed.
The cube root of 81 is 4.32674871092
Assume Charles charges $7*3=$21 if he babysits for 2,5 hours (that is 2 and a half hours).
That is we are not considering Charles babysitting exactly 1, 2, 3 or 4 hours, but also in between times.
then we can write the following piecewise function to describe the situation:
f is a function from (0, 4] to {$7, $14, $21, $28}
9 because it's the gcf (greatest common factor)