Answer:
A = 2.1
B = 5.9
C = 10
D = 0.9
Explanation:
This is a long one
A + B = 8
my plan is to substitute B
B - D = 5
B = 5 + D
Now substitute D
C*D=9
D = 9/C
Now substitute C
A*C = 21
C = 21/A
Back to the D equation
D = 9/C
D = 9/(21/A) = 9A/21 = 3A/7
Back to B equation
B = 5 + D
B = 5 + 3A/7
Back to A equation
A + B = 8
A + (5 + 3A/7) = 8
7/7A + 3/7A + 5 = 10A/7 + 5 = 8
10A/7 = 3
10A = 21
A = 21/10 = 2.1
The rest should be simple
B = 5 + 3A/7
B = 5 + 3(2.1)/7 = 5.9
C = 21/A
C = 21/2.1 = 10
D = 9/C
D = 9/10 = 0.9