Timmy's Taxi Service charges a flat fee of $1.50, plus an additional fee for each mile of travel. A 5 mile trip costs $11.50 and a 9 mile trip costs $19.50. Which statement is true about the relationship between miles and cost?

Group of answer choices

The relationship is linear because it increases at a constant rate of change of $2 per mile.

The relationship is linear because it increases at a constant rate of $8 per mile.

The relationship is exponential because it increases at a changing rate of $2 per mile.

The relationship is exponential because it increases at a changing rate of $8 per mile.