Answer:
79
Step-by-step explanation:
There is a cool easy way to solve this kind of problem. If a range is given, and the entire range increases in incrememnts of 1, then you can find the number intergers inclusive by taking the first number and subtracting it from the last and adding 1. Since in this problem you want it exclusive, we can rewrite the range to 21-99.
99-21 +1 = 78 + 1 = 79
