bonjour,
a) 3x + 1 - 4x = 7
-x+1 = 7
-x = 7-1
-x = 6
x =-6
b) 2x + (3x-6) = x+10
2x+3x-6 = x+10
5x-6 = x+10
5x-x = 10+6
4x = 16
x = 4
c) 5 - (3x - 11) = -8x - 4
5-3x+11 =-8x-4
-3x+16 = -8x-4
-3x+8x =-4-16
5x =-20
x =-4
d) -(x+3) - (-8x + 12) = 13
-x-3+8x-12 =13
7x-15 = 13
7x = 13+15
x = 4