We want to know how money Jessie's friend would need if he wants to ride 6 rides.
We know that the Amusement Park charges a $7 admission fee plus $1.75 per ride. We can write this as:

Where y is the cost of doing x rides on the amusement park. If we want to find the cost for 6 rides, then we should replace x for 6, and we get:

This means that the cost of Jessie's friend for 6 rides would be $17.5.