7. X + 2y = 4 (move x beside 4, since it's positive it will be negative)
2y = 4 - X (divide terms to 2)
| 2y ÷ 2 = y | 4 ÷ 2 = 2 | -X ÷ 2 = -1/2 (There's always an imaginary 1 beside x, only just x).
y = 2 - 1/2x (rearrange terms)
y = -1/2x + 2
9. -2x + 3y = -6 (move -2x beside -6, since it's negative it will turn into a positive)
3y = -6 + 2x (divide by 3)
y = -2 + 2/3x (rearrange)
y = 2/3x -2
11. 5x - 2y = 14
-2y = 14 - 5x (-2 ÷ -5x is 5/2x, but since numerator and denominator are negative, fraction turns positive)
y = -7 + 5/2x
y= 5/2x - 7
13. 4x + 3y = 12
3y = 12- 4x
y = 4 -4/3x
y = -4/3x + 4
15. x + 3y = -3
3y = -3 -x
y = -1 -1/3x
y -1/3x - 1
There you go!
Just remember those steps and you should be fine :)