А) -15х + 31 = -7 + 4х; -15х + 31 + 7 = 4х; -15х + 38 = 4х; 38 = 4х + 15х; 38 = 20х; х = 38:20; х = 1,9. б) 11 - х = 55 + х; 11 - 55 = х+х; -44 = 2х; х = -44:2; х= -22. в) 28 - 4x = 19 - х; 28 - 4х + х = 19; 28 - 3х = 19; 28 - 19 = 3х; 9 = 3х; х= 9:3; х = 3. г) -35 - 2х = 42 + 9х; -35 - 42 = 9х + 2х; - 77 = 11х; х = -77:11; х = -7.