Is there more to this problem? By saying f(4), you'd be inputting a 4 for every variable x. There is not enough info here to answer the question.
The answer is 14%
Cost of meal is 100%: $18.50 is 100%
Tip is x%: $2.59 is x
Make a proportion:
$18.50 : 100% = $2.59 : x
x = 100% * $2.59 : $18.50
x = 14%
4.the dot would be on 1 1/2 and the x would be pointing toward the negative numbers
