Question

18+12/11 = 15 + X/X
$\frac{18 + 12}{12} = \frac{15 + x}{x}$
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Answer 1

$\frac{18}{12} + 1 = \frac{15}{x} + 1 \\ \frac{3}{2} = \frac{15}{x} \\ 3x = 30 \\ x = 10$