Math
posted by Tyler .
5x6=5x4+5xb

It is hard to know what "x" indicates. Typically it is an unknown, so online "*" is used to indicate multiplication. However, if it is "5x to the 6th power," it would be indicated as "5x^6". Online "^" is used to indicate an exponent. If both the number and the unknown are raised to the power, it should be written "(5x)^6".
Clarify your equation and what your question is. 
Do you mean:
(5*6) = (5*4) + 5b (?) If so,
30 = 20 + 5b
10 = 5b
2 = b