Part A
the total cost is
3*(31.99)+2*(13.80)=$123.57
answer part a is $123.57
Part B
we have that
the total cost using the coupon is
123.57-10=$113.57
Using proportion
Remember that
123.57 represent 100%
so
100/123.57=x/10
solve for x
x=10*100/123.57
x=8%
answer is 8%
Part 2
with paying 7% tax
the total cost is $123.57
Remember that
100%+7%=107%=107/100=1.07
so
the total cost is
$123.57(1.07)=$132.22