Marie and Charles make monthly mortgage payments of $1,500, pay property taxes of $3,000 a year, and owe $5,000 on their credit cards on which their average minimum payment is $250. They also have a car loan which costs them $550 a month. Their combined gross pay is $140,000 a year and their take-home pay totals $102,000. What is their GDS ratio? 

a) 20.6% 

b) 15.0% 

c) 21.9% 

d) 30.0%