Incorrect. I misinterpreted the problem as the number of different sequences of the last 5 fireworks out of the 15 available. Rather, those five were already determined. Therefore, instead of the number of permutations of 15 items arranged 5 at a time, the problem asks for the number of ways to arrange the remaining 10 fireworks.
Approximately correct. Overlooking the last sentence, which asks for the answer to be rounded to the nearest tenth, I instead rounded up to the nearest whole number.