Its just an application of the distribution property of multiplication
ex.
A (B+C) = A*B + A*C
you're given
[tex]\frac{5}{6} x +b = \frac{1}{6} (5x+2)[/tex]
when you distribute the 1/6 on the right side, you get
[tex]\frac{5}{6} x +b = \frac{1}{6} *5 x + \frac{1}{6} *2[/tex]
well
[tex]\frac{1}{6} *5 = \frac{5}{6}[/tex]
cancel out the 5/6x on both sides, you are left with
[tex]b= \frac{2}{6}[/tex]
