3) 3,8 : (4c + 3) = 2 : $$2\frac{2}{19}$$;

Решим уравнение:

$$\frac{3,8}{4c + 3} = \frac{2}{2\frac{2}{19}}$$.

$$\frac{3,8}{4c + 3} = \frac{2}{\frac{40}{19}}$$.

$$\frac{3,8}{4c + 3} = \frac{2 * 19}{40}$$.

$$\frac{3,8}{4c + 3} = \frac{19}{20}$$.

$$4c + 3 = \frac{3,8 * 20}{19}$$.

$$4c + 3 = \frac{38 * 2}{19}$$.

$$4c + 3 = 2 * 2$$.

$$4c + 3 = 4$$.

$$4c = 1$$.

$$c = \frac{1}{4} = 0,25$$.

Ответ: $$c = 0,25$$.