Excel formulas

Hi I am new to making spreadsheets on excel, i also have a mac and using the excel on my mac. 

I am trying to add how much we make for the type of treatment we provide. 

for instance we have 3 types of things we bill for, OP, IOP, PHP

i want OP to equal 375 and have it say OP instead of having to put 375 in the cell 

i want IOP to equal 1295 and have it say IOP instead of having to put 1295 in the cell

i want PHP to qual 1595 and have it say PHP instead of having to put 1595 

and then want it to calculate for the 5 days of services to see what we made that week and have it in the the last column i put that says total billing. 

how would i do that with it still saying OP, IOP or PHP instead of the amount?