3. Найдите сумму подобных слагаемых: a) -7x + 15x - 8x б) 1,3y - 2,8y - 1,2y + 0,7y в) $-2\frac{3}{8}a + 1\frac{1}{4}a - 1\frac{1}{8}a + \frac{3}{4}a$

a) -7x + 15x - 8x = (-7 + 15 - 8) * x = (8 - 8) * x = 0 * x = 0 б) 1,3y - 2,8y - 1,2y + 0,7y = (1,3 - 2,8 - 1,2 + 0,7) * y = (2 - 4) * y = (-2) * y = -2y в) $-2\frac{3}{8}a + 1\frac{1}{4}a - 1\frac{1}{8}a + \frac{3}{4}a = -\frac{19}{8}a + \frac{5}{4}a - \frac{9}{8}a + \frac{3}{4}a = (-\frac{19}{8} + \frac{10}{8} - \frac{9}{8} + \frac{6}{8})a = (\frac{-19+10-9+6}{8})a = (\frac{-12}{8})a = -\frac{3}{2}a = -1,5a