Final answer:
The fitness center charges a one-time sign-up fee of $59 and a monthly membership fee of $13 as represented by the equation y = 13x + 59, where x is the number of months.
Step-by-step explanation:
The equation y = 13x + 59 represents the total cost of a fitness center membership after x months.
In this equation, 59 is the one-time sign-up fee, which is also the y-intercept, and 13 is the monthly membership fee, which is the slope.
So, the complete statement is: The fitness center charges a one-time sign-up fee of $59 and a monthly membership fee of $13.