Each ride has a fixed cost of 7 and a cost that increases proportionally to the distance travelled of 0.25 per mile. Therefore the total cost of the ride is:

Where "x" is the distance in miles. Marco can only spend 30 on his ride, therefore the cost must be less or equal to that value.

We can solve the linear equation by isolating the "x" variable on the left side.

Marco's travel must be shorter or equal to 92 miles.