7. Let x be the money she began with, then
1/3 (x - 4/5 x) = 15
1/3 (1/5 x) = 15
1/15 x = 15
x = 15 * 15 = $225
Therefore, she started with $225
Let x be the number of students surveyed, then
1/2(x - 1/3x - 1/6x) = 9
1/2(1/2x) = 9
1/4x = 9
x = 4 * 9 = 36
Therefore, the number of students surveyed is 36.