-0.4(3x-0.5)-0.7=1.3(2x-15)

Найдем корень уравнения.

-0.4 * (3 * x - 0.5) - 0.7 = 1.3 * (2 * x - 15); 

Раскроем скобки. 

-0.4 * 3 * x - 0.4 * (-0.5) - 0.7 = 1.3 * 2 * x - 1.3 * 15; 

-1.2 * x + 0.4 * 0.5 - 0.7 = 2.6 * x - 19.5; 

-1.2 * x + 0.2 - 0.7 = 2.6 * x - 19.5; 

-1.2 * x - 0.5 = 2.6 * x - 19.5; 

-1.2 * x - 2.6 * x = -19.5 + 0.5; 

x * (-1.2 - 2.6) = -19; 

x * (-3.8) = -19; 

-3.8 * x = -19; 

3.8 * x = 19; 

x = 19/3.8; 

x = 190/38; 

x = 10/2; 

x = 5.