if $\frac{x+4}{x+3} = 4$, find the value of $\frac{1}{x+3}$.
x + 4
_____ = 4 multiply through by x + 3
x + 3
x + 4 = 4 ( x + 3)
x + 4 = 4x + 12
x - 4x = 12 - 4
-3x = 8
x = -8/3
So
1 / ( x + 3) = 1 / ( -8/3 + 3) = 1 / ( 1/3) = 3
