Can you guys help me solve these math questions?

Question

1. -2z - xy = x + 7 (finding x) 
2. a/b - 8 = c/d (finding a) 
3. 6pr + 7rs -2st = -9 (finding r) 
4. p = (m+n/-5) (finding n) 

Answer 1

1)

- 2z - xy = x + 7

Add (xy - 7) to each sides

- 2z - xy + xy - 7 = x + 7 + xy - 7

- 2z - 7 = x + xy

x + xy = - 2z - 7

x ( 1 + y) = - (2z + 7)

x = - (2z + 7)/(1 + y)

Solution : x = - (2z + 7)/(1 + y)

Answer 2

2)

a/b - 8 = c/d

Add 8 to each side.

a/b - 8 + 8 = (c/d) + 8

a/b = (c/d) + 8

Multiply b to each side.

(a/b)b = b [ (c/d) + 8 ]

a = bc/d + 8b

Solution : a = bc/d + 8b

Answer 3

3)

6pr + 7rs -2st = -9

Add 2st to each side.

6pr + 7rs - 2st + 2st = - 9 + 2st

6pr + 7rs = 2st - 9

(6p + 7s)r = 2st - 9

r = (2st - 9)/(6p + 7s)

Solution : r = (2st - 9)/(6p + 7s).

Answer 4

4)

p = (m+n)/-5

Multiply each side by -5.

(-5)p = (-5)(m+n)/-5

-5p = (m+n)

m+n = -5p

n = - 5p - m

Solution : n = - 5p - m.