[tex] \frac{4}{12} = \frac{10}{x} \\ \\ \frac{1}{3} = \frac{10}{x} \ / \ simplify \\ \\ \frac{1}{3} x = 10 \ / \ multiply \ each \ side \ by \ x \\ \\ \frac{x}{3} = 10 \ / \ simplify \\ \\ x = 10 \times 3 \ / \ multiply \ each \ side \ by \ 3 \\ \\ x = 30 \ / \ simplify \\ \\ [/tex]
The final result is C) 30.
