Let Michelle be x.
Jeremy has 5 more than Michelle = x +5
Carlos has 10 more than Jeremy = (x+ 5) + 10 = x + 15
Together they all have $80
x + (x+5) + (x+15) = 80
x + x + x + 5 + 15 = 80
3x + 20 = 80
3x = 80 - 20
3x = 60
x = 60/3 = 20
Michelle has x, which is = 20
Michelle has $20.