The Newberg Tigers are having team shirts made. One option is to pay Reggie's Tees a $40 setup fee and then buy the shirts for $4 each. Another option is to go to City Printing, paying $20 for a setup fee and an additional $8 per shirt. The team parent in charge of the project notices that, with a certain number of shirts, the two options have the same cost. How many shirts is that?