Question 666188
Given
A = 3B
B = x+2
A+B=128
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Substitute
Substitute A and B into the last equation, such that 
3B + B = 128 
so
3(x+2) + x+2 = 128
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Distribute the 3
3x + 6 + x+2 = 128
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Combine like terms
4x + 8 = 128
4x = 120
{{{highlight(x = 30)}}}

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