24. 4 7^(3x) = 5√49.

$$7^{3x} = \sqrt[5]{49}$$

$$7^{3x} = (7^2)^{\frac{1}{5}}$$

$$7^{3x} = 7^{\frac{2}{5}}$$

$$3x = \frac{2}{5}$$

$$x = \frac{2}{15}$$

Ответ: $$x = \frac{2}{15}$$