I believe you want to know how much each of them SAVED.
Let the amount saved by Michelle be x, the amount saved by Sam be y and the amount saved by Dean be z.
From the givens:
x = 3y (Michelle saves 3 times as much as Sam).......eq1
y = 2+z (Sam saves 2$ more than Dean)
z=y-2.........eq 2
x+y+z = 240 (total amount)......eq 3
substitute by equation 1 in 3:
3y+y+z=240
4y+z=240......eq 4
substitute by 2 in 4:
4y+y-2=240
5y=242
y= 48.4$
from 1:
x=3y
x=145.2$
from 2:
z=y-2
z=46.4$
