8 and 3/4 of a chore
she needs to earn 13.50-$3=10.50
divide 10.50 by 1.20 to get the amount of chores she needs to do.
the answer is 8 and 3/4 of a chore
they do have enough to pay for their dinner including dinner tax and gratuity
so they have $30.
their dinner costs $21
taxes are $21 *1.06=22.26
tip is 22.26*1.15=25.599
so they do have enough to pay for their dinner