Acafe has a few tables that seat 6 people. there are also a few tall tables that seat 4 people. there are 7 waiters, 1 manager, and 1 cashier present in the cafe. if all the tables are full, the expression 6x + 4y + 7 + 1 + 1 gives the total number of people in the cafe where x represents the number of six-top tables and y represents the number of four-top tables. an equivalent of this expression is .