Question

Solve S = 2ab + 2bc + 2ac for b

Answer 1

 A = 2ab + 2ac + 2bc 
A = 2b(a + c) + 2ac 
2b(a + c) = A - 2ac 
b = (A - 2ac) / [2(a + c)]

Answer 2

Take b as a common factor
s=b (2a + 2c) +2 ac


s-2ac=b (2a+2c)
b=(s-2ac)/(2a+2c)