Assuming the order does not matter, you want the number of combinations of 9 things taken 5 at a time. The combinations can be shown as C(9,5), 9C5.
C(9, 5) =
9/5(9-5) =
9*8*7*6*5 / 5*4
The 5 terms cancel.
9*8*7*6 / 4*3*2 =
9*7*2 =
126
The above change is because 4*2 cancels the 8 in the numerator and 6/3 = 2
Therefore, the solution is 126.