Making groups of levels

[ropr]

Hi, everybody
i have one excel file containing lot of different digits (example 5,7,10,11,15,16,19,20,23) in one row(a2 to a301). Each number in different cells. Now i want to add another row to same sheet for making group (low level, medium level, high level). The low level is 7 & less than 7, medium level is 7 to 15, high level is 16 & above. For these calculation i want to give three letters for low, medium, high respectively 1,2,3. Can anyone please help me.