Equations

1.
A - 10
B - -20
C - -10
D - -15

2.
A - 18
B - -20
C - -10
D - -18

3.
A - All numbers.
B - -1
C - 4
D - 28

4.
A - -1.5
B - -3.5
C - 1.5
D - -1.9