She ate only one lunch, so the cost of the lunch is a constant - it is the 9
9 - cost of lunch
Now, we don't know how many rides she took- it will be represented by a variable, x,
x-number of rides
and each ride must have cost 1.5
1.5- cost of each ticket
so 1.5x was the total cost of the ride tickets
and 1.5x+9 is the total cost!