Answer:
A = a + b + c + d
c = A - a - b - d
A-a-b-d =c
Step-by-step explanation:
A=a+b+c+d
We want to get c alone
Subtract a from each side
A-a = a+b+c+d -a
A-a = b+c+d
Subtract b from each side
A-a -b = b+c+d-b
A-a -b = c+d
Subtract d from each side
A-a-b-d = c+d-d
