An airport has two long-term parking lots. The cost to park, y, in each lot for x days is shown in the tables.

Lot A
Days Parked Cost
1 $16
2 $20
3 $24
4 $28
Lot B
Days Parked Cost
1 $6
2 $12
3 $18
4 $24

A system of linear equations can be used to determine on which day the cost to park is the same for both lots. One of the equations in the system is y = 6x. What is the other equation in the system?