1) Найдем длину стороны PX:
$$PX = MP - 10\frac{21}{27} = 17\frac{14}{27} - 10\frac{21}{27} = 16\frac{14 + 27}{27} - 10\frac{21}{27} = 16\frac{41}{27} - 10\frac{21}{27} = (16 - 10) + \frac{41 - 21}{27} = 6\frac{20}{27} \text{ дм}$$2) Найдем длину стороны MX:
$$MX = MP + 4\frac{26}{27} = 17\frac{14}{27} + 4\frac{26}{27} = (17 + 4) + \frac{14 + 26}{27} = 21 + \frac{40}{27} = 21 + 1\frac{13}{27} = 22\frac{13}{27} \text{ дм}$$3) Найдем периметр треугольника MPX:
$$P = MP + PX + MX = 17\frac{14}{27} + 6\frac{20}{27} + 22\frac{13}{27} = (17 + 6 + 22) + \frac{14 + 20 + 13}{27} = 45 + \frac{47}{27} = 45 + 1\frac{20}{27} = 46\frac{20}{27} \text{ дм}$$Ответ: Периметр треугольника MPX равен $$46\frac{20}{27}$$ дм.