$24 x 6 = 144 Minus the $6 she spent per week -$36 = $108
I guess that is what you meant when you typed "she saved $24 each week she saves $6???
You may go the super easy way and choose 1 as the whole number and 0.28 as the decimal number. Then you'd obviously have 
Otherwise, to be a bit more creative, you can observe that

And since 1/25=0.04, you can also choose 7 as the integer, and 0.04 as the decimal to get

7 4-credit classes. 4 3-credit classes.
7*4 = 28, and 4*3 = 12. 11 classes, and 40 credits.
The answer to your question is " D.)119"