4. 15 -- + -- 25 4

$$ \frac{4}{25} + \frac{15}{4} = \frac{4 \cdot 4 + 15 \cdot 25}{25 \cdot 4} = \frac{16 + 375}{100} = \frac{391}{100} = 3\frac{91}{100} $$

Ответ: $$3\frac{91}{100}$$