So, in the situation when she still had the 50 students, the sum of their heights was
50*68=3400 (you can pretend here that all the students are 68 inches tall)
She subtracted the outliners:
3400-82-86=3232, so the new sum is 3232.
She now has to divide it by the number of the students which is now lower by 2: 48
So, 3232/48=67,33
the new mean is 67,33!