Something is wrong with the problem. It is not possible for a ride to cost $10.50. 11 quarter miles would have cost $2.50 for the first quarter mile and $0.75 for 10 additional quarter miles. $2.50 + 10x$0.75 = $2.50 + $7.50 = $10.00 12 quarter miles would have cost $2.50 for the first quarter mile and $0.75 for 11 additional quarter miles. $2.50 + 11x$0.75 = $2.50 + $8.25 = $10.75 So the $10.50 had to be a typo. You can give the correct value in the thank-you note form below and I'll get back to you. Edwin