Let
Total Bill = $x
Given
Jen paid = $8
Heather paid = x(3/5)=$3x/5
Total Bill=Jen Paid + Heather Paid
x=8+3x/5
Multiply by 5 both sides
5x=40+3x
5x-3x=40
2x=40
2x/2=40/2
x=20
3/5 of 20 = (3/5)(20)= 3*4 = 12
Bill was for $20 Jen paid $8 and remaining $12 paid by Heather.