−7(3m − 8) + 5(6m − 7) при m = 3
−7(3m − 8) + 5(6m − 7) = −21m + 56 + 30m − 35 = 9m + 21
при m = 3:
9m + 21 = 9 * 3 + 21 = 27 + 21 = 48

−1,2(2a − 3) − (4 − 5a) − 0,6(1 − a) при a = −2,5
−1,2(2a − 3) − (4 − 5a) − 0,6(1 − a) = −2,4a + 3,6 − 4 + 5a − 0,6 + 0,6a = 3,2a − 1
при a = −2,5:
3,2 * (−2,5) − 1 = −8 − 1 = −9

$\frac{5}{12}(4,8x - 1\frac{1}{5}y) - 5,4(\frac{4}{9}x + 1,5y)$ при x = 4, $y = -1\frac{2}{43}$
$\frac{5}{12}(4,8x - 1\frac{1}{5}y) - 5,4(\frac{4}{9}x + 1,5y) = \frac{5}{12}(\frac{48}{10}x - \frac{6}{5}y) - \frac{54}{10}(\frac{4}{9}x + \frac{15}{10}y) = \frac{5}{12}(\frac{24}{5}x - \frac{6}{5}y) - \frac{27}{5}(\frac{4}{9}x + \frac{3}{2}y) = \frac{5}{12} * \frac{24}{5}x - \frac{5}{12} * \frac{6}{5}y - \frac{27}{5} * \frac{4}{9}x - \frac{27}{5} * \frac{3}{2}y = \frac{1}{1} * \frac{2}{1}x - \frac{1}{2} * \frac{1}{1}y - \frac{3}{5} * \frac{4}{1}x - \frac{81}{10}y = 2x - \frac{1}{2}y - \frac{12}{5}x - 8,1y = 2x - 0,5y - 2,4x - 8,1y = -0,4x - 8,6y$
при x = 4, $y = -1\frac{2}{43}$:
$-0,4 * 4 - 8,6 * (-1\frac{2}{43}) = -1,6 - \frac{86}{10} * (-\frac{45}{43}) = -1,6 - \frac{43}{5} * (-\frac{45}{43}) = -1,6 - \frac{1}{1} * (-\frac{9}{1}) = -1,6 + 9 = 7,4$