Answer:
f(x) = 2+2*x where x is the miles you run
Explanation:
Lets call f(x) the function that show how much money the sponsor will give you as a function of the miles you walk (x). If you do not walk any mile you have only $5, then if you walk one mile you get $5+$2=$7, and so on. Lets use a simple table for some values (I will omit $ symbol for simplicity):
x (miles) f(x) (money)
1 5+2
2 5+2(2) = 9
3 5+3(2) = 11
10 5+10(2) = 25
x 2+2*x
So we can observe a pattern, the total payment you receive will be 5 plus the miles you run multiplied by 2. Thus the expression for the total amount you will collect from your sponsor at the end of the walk a thon is:
f(x) = 2+2*x
where x is the miles you run.
I hope it is understandable.