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a) 4(x +5) = 10x +3
4x +20 = 10 x +3
4x -10x = 3 -20
-6x = -17
x = 17/6

b) 3x - 6 = 6x +24
3x -6x = 24 +6
-3x = 30
x = -10

7x -5x -3 = 5x - 15 +2
7x -5x -5x = - 15 +2 +3
-3x = -10
x= -10/3

7n +14 -3 =  25 -3n -4
7n +3n = -4 +3 -14
10 n = -15
n = -15/10 = - 3/2

4y + 12y - 6 = 3y +3
16y -3 y = 3 +6
13y = 9
y = 9/13