the fixed entry is 18 $
and per ball price is 0.08 $
so the equation of expenditure is 18 + 0.08 B
here, B = no. of balls
to get the promotion offer she needs to spend 75 $ or more
so total expenditure should be 75$ or more in order to get the offer.
that is

so the answer is option B
2)
for the smallest number of paintballs that Carolina can buy along with the entrance fee to get the promotion is

so the no. of the balls are 713 in order to get the promotion of 75 $