Найти x из пропорции 2:3=(5x-7):12
2:3 = (5x - 7):12;
5x - 7 = (2*12) : 3;
5x - 7 = 2 * 4;
5x - 7 = 8;
5x = 8 + 7;
5x = 15;
x = 15 : 5;
x = 3;