Fourth box is DF. For this one the last sentence basically gives you the answer.
Just so you know for the fourth I guessed on if it's DF lined or DF unlined. I made my educated guess on the fact that the last line doesn't have a line. I hope this helps, and please tell me if I got something wrong, or my explanation wasn't sufficent enough for you.
They have $49.00 left for desert because a ticket is $15 for each person 7 and older. So 15 × 3 people = $45.00. $1.50 per slice and they got 4 slices so 1.50 × 4 = $6.00. $45.00 + $6.00 = $51.00. $100 - $51 = $49.00