[tex]300\ miles\ on\ 12,5\ gallons\\
x\ miles\ \ on\ \ \ 42\ gallons\\\\
Making\ proportion:\\
300-12,5\\
x-42\\\\
Cross\ multiplication\\
300*42=12,5x\\\\12600=12,5x\ \ \ | divide\ by\ 12,5\\\\
x=1008\\\\
He\ can\ drive\ 1008\ miles\ on\ 42 \ gallons\ of\ gas.[/tex]
