First you need to remove the fractions from each side,
take the equation: (x+1)/(x+3) = (2x-1)/(3x-1)
now multiply by x+3 to give x+1 = (2x-1)(x+3)/(3x-1)
now multiply by (3x-1) to give (3x-1)(x+1)=(2x-1)(x+3)
Then expand out the brackets
3x2 +2x-1 = 2x2 +5x-3
as x2 appears on both sides, subtract (2x2 +5x-3) from both sides to give x2 -3x +2=0 which can now be solved to give values of x
factorise to give (x-2)(x-1)=0
therfore x= 2 or x=1