You will have to get ride of the denominator first then isolate the variable. I will use x as big A since theres no capital letters in equation mode:
[tex]x = \frac{a + b + c}{3} \\ 3x = a + b + c \\ 3x - a - c = b[/tex]
So b is
[tex]b = 3x - a - c[/tex]
Remember I used x as big A in the equation.
