Brother one: x
Brother two: x + 15
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Make them add up to 55 in an equation.
x + (x + 15) = 55
Combine like terms.
2x + 15 = 55
Subtract 15 from both sides.
2x = 40
Divide both sides by 2.
x = 20
Plug 20 for x into brother two.
(20) + 15 = 35
Brother one has saved $20, brother two has saved $35.