Find the value of $x$ in each of the following proportions. Show all calculations.
(1) $\frac{2}{3} = \frac{x}{12}$
(2) $x : 15 = 6 : 10$
(3) $\frac{3}{7} = \frac{9}{x}$
(4) $12 : x = 4 : 9$
(1) $\frac{2}{3} = \frac{x}{12}$
(2) $x : 15 = 6 : 10$
(3) $\frac{3}{7} = \frac{9}{x}$
(4) $12 : x = 4 : 9$