15. б) $$1\frac{1}{2} - x = \frac{3}{4}$$

б) $$1\frac{1}{2} - x = \frac{3}{4}$$ $$\frac{3}{2} - x = \frac{3}{4}$$ $$ x = \frac{3}{2} - \frac{3}{4}$$ $$ x = \frac{6}{4} - \frac{3}{4}$$ $$ x = \frac{3}{4}$$ Ответ: $$\frac{3}{4}$$