aound 15 or it depends how many slices there were in the first place
F=5 dollar bills
t=twent dollar bills
38 total bills
f+t=38
400 in bills
400=5f+20t
we have
f+t=38
5f+20t=400
multipy first equation by -5 and add to second equation
-5f-5t=-190
5f+20t=400 +
0f+15t=210
15t=210
divide both sides by 15
t=14
subsitute
t+f=38
15+f=38
f=23
23 five dolar bills
15 twenty dollar bills