To determine how far Santiago can travel on 19 gallons, we first need to calculate the fuel efficiency of his car in miles per gallon (mpg).
First, we find the miles per gallon by dividing the distance traveled by the number of gallons used:
\[ \text{Fuel efficiency (mpg)} = \frac{\text{Distance}}{\text{Gallons}} = \frac{525 \text{ miles}}{15 \text{ gallons}} = 35 \text{ mpg} \]
Now that we know the car's fuel efficiency is 35 miles per gallon, we can calculate the distance he can travel on 19 gallons by multiplying the fuel efficiency by the number of gallons:
\[ \text{Distance} = \text{Fuel efficiency} \times \text{Gallons} = 35 \text{ mpg} \times 19 \text{ gallons} = 665 \text{ miles} \]
Therefore, Santiago can travel 665 miles on 19 gallons.