-10=b4 <----- Write your equation out
-10=[tex]\frac{b4}{4}[/tex] <----- Divide b4 by 4 to get b by itself.
[tex]\frac{-10}{4}[/tex]=b <----- Divide -10 by 4 because what you do to one side, you mjst do to the other.
-2.5=b <----- There is your answer; -2.5
