Answer:
9 hours
Step-by-step explanation:
"At the same rate" means time and wages are proportional.
time/wages = t/$108 = (13 h)/$156
t = 108(13 h)/156 . . . . . . . . . . . . . . . units of dollars cancel
t = 9 h
Chang would have to work 9 hours to make $108.
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}
ANSWER

EXPLANATION
The given function is:

Factor -3 for the first 2 terms.

We add and subtract the square of the coefficient of x.

Factor the perfect square trinomial.

The vertex form is:

10/52 or when reduced, is 5 over 26 (5/26) and if they want it as a percent, its 19% (.19)