Answer is at a monthly rate more than > 20 months the flat fee of $500 is the better choice
Step by step
25 per month = $500 flat fee
25x = 500
Divide both sides by 25 to solve for x
25/25 x = 500
Monthly membership at = 20 months of a per month membership to equal the flat rate cost of $500
Monthly membership more than > 20 months the flat fee of $500 is the better choice
Monthly membership less than < 20 months it is cheaper to have the per month membership