At the bank there a 4 lines with 7 customers and there are five customers left over. How many
customers are there?

Explanation:

According to the given information,

There are 4 lines with 7 customer each, so to calculate the "total number of customers",

(one line with 7 customer so 4 line = ?)

4 * 7 =28

Total customers = 28

There are 5 customer who are left. So the "number of customers" whose service is done can be calculated as,

28-5 = 23

Customer serviced = 23

Left out customer = 5