Which system of linear equations represents the situation?
 The Martin family pays $12 per hour to a babysitter. They also give her
 a $7 tip. The Bagley family pays $15 per hour to a babysitter. The
 Bagley family's babysitter pays $8 to order a pizza.
 Let h represent the number of hours of babysitting and m represent
 the total amount of money each babysitter earns.