The Robinson family is looking to rent a large truck for their upcoming move. With Barbara's Moving, they would pay $50 for the first day plus $2 per additional day. With Lowell Rent-a-Truck, in comparison, the family would pay $20 for the first day plus $8 per additional day. Before deciding on which company to use, Mrs. Robinson wants to find out what number of additional days would make the two choices equivalent with regards to cost. How many additional days would that be?