#### Answer

She has 15 ones, 3 fives, and 6 twenty dollar bills.

#### Work Step by Step

Let o be the number of ones, f be the number of fives, and t be the number of twenty dollar bills. Thus, we obtain:
$ o + t + f = 24 \\ o + 20t + 5f = 150 \\ t = 2f$
We know from equation one that $o = 24 - t -f.$ We plug this into equation two to find:
$ 24 + 19t + 4f = 150 $
We plug in equation three to find:
$ 38f + 4f = 126 \\ 42f = 126 \\ f =3$
Thus, we find:
$ t = 2f = 2(3) = 6 $
Since there are 24 bills, we find:
$ o = 24 - 6 -3 = 15$