To subtract similar rational expression, change the sign of each term in the subtrahend, then proceed to addition rule by combining only the numerators then copy the denominator, since they are similar rational expressions meaning same denominator.
Example: 3x + 2 - 5x + 6
Change the sign of each term in subtrahend 5x + 6
Becomes: 3x+2 + (-5x -6)
Combine like terms in denominator, then copy the denominator
Final answer: -2x-4