Given that:
Membership feet to play indoor soccer at the Sun Oaks Club = $100
Hourly rate = $10
To find:
The function f represents the cost of playing soccer at Sun Oaks.
Here, fixed cost is $100.
Let the number of hours of playing be t. So, total variable cost is $10t.
Total cost = Fixed cost + Variable cost

So, the required function is
.
Now, if the hourly rate were halved. Then,
Hourly rate 
So, total variable cost is $5t and total cost function is

So, the required function is
.