Find the unknown number in each equation.
5a-3a= 18
a=
5a-3a= 18
2a = 18
Divide both sides of the equation by 2.
a = 9
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You can prove this by substituting 9 for a in the original equation.
5(9) - 3(9) = 18
45 - 27 = 18
Yep!! It's right.