The price of a gym membership has a one-time sign-up fee and a monthly fee. the price can be modeled by the function y = 10x + 15, where x is the number of months. what is the y-intercept, and what does it represent? 10; it represents the monthly fee 10; it represents the one-time sign-up fee 15; it represents the monthly fee 15; it represents the one-time sign-up fee