you want to isolate a for when solve the equation for a
a(x − b) − 2k = L
you get everything away from a
add 2k to both sides of the equation
a(x − b) − 2k + 2k = L + 2k
since
− 2k + 2k is 0, then the left side is
a(x − b) = L + 2k
then we divide both sides by x - b to cancel out x - b on the leftside
a = (L+2k)/(x − b)
or [tex]a = \displaystyle\frac{L+2k}{x-b}[/tex]