Question

х + 3х = 7 + 5
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Answer 1

х + 3х = 7 + 5

4х=12

х=3

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Answer 2

$x + 3x = 7 + 5 \\ x = 3 \\ x + 3x = 7 + 5 \\ 4x = 12 \\ x = \frac{12}{4} = 3$