Josefina works between 10 and 30 hours per week at a pizzeria. She earns $6.50 an hour, but can earn tips when she delivers pizza.

a) Write a system of inequalitites to represent the dollars 'd' she could earn for 'h' hours in a week.

b) If Josefina recieved $17.50 in tips and earned a total of $180 for the week, how many hours did she work?