Final answer:
The yy-intercept of the equation c=45t+100 for gym membership cost is 100, representing the initial one-time joining fee for the gym.
Step-by-step explanation:
The yy-intercept of the equation c = 45t + 100 is 100. This is interpreted as the one-time fee to join the gym because it is the cost (c) when the number of months (t) is 0. As you increase the value of t, you are adding on the monthly fees, which is represented by the 45 multiplied by t. Hence, the yy-intercept (the constant term without t) is the initial cost to start the gym membership, and the number 45 (the coefficient of t) represents the monthly fee.