peg spends $7.50 a week for grapefruit. When grapefruit are out of season, she gets 1 fewer grapefruit than when they are in season. If the price decreases by $3 per dozen in season, how many dollars will it cost her to buy a dozen grapefruit out of season?

Since we are apparently dealing with exact integers here, look it like this:

750 = 5*5*5*6

750 = 125 * 6 = 150 * 5

So, if grapefruits cost $1.25 in-season, and $1.50 out of season, then

In season she gets 6/week
Out of season she gets 5/week.
and a dozen costs $3 more out of season.