л) 8 (250: c + 12) = 136

л) Решим уравнение: $$8 \cdot (250 : c + 12) = 136$$$$250 : c + 12 = \frac{136}{8}$$$$\frac{250}{c} + 12 = 17$$$$\frac{250}{c} = 17 - 12$$$$\frac{250}{c} = 5$$$$5c = 250$$$$c = \frac{250}{5}$$$$c = 50$$

Ответ: 50