[tex] \frac{5}{4} = \frac{15}{x + 5} \\ \\ \to \: x + 5 = \frac{15 \times 4}{5} \\ \\ \to \: x + 5 = 3 \times 4 \\ \\ \to \: x + 5 = 12 \\ \\ \to x = 12 - 5 \\ \\ \to \: x = 7[/tex]
