It's basically asking you if the number of towers for each 1 thousand customers is the same for all the rows in the table.
if you divide the towers in each row by the customers:
252/5.25 , 300/6.25, etc.
you will see that each of them have 48 towers for every 1 thousand customers.
Therefore, the ratios of towers to customers are all equal and the unit ratio is 48.