Replacing text with a value?

Hello,
So I'm wanting to make a rota for work as I'm a midwife, what I'd like to do is the following:
C is community and adds up to approximately 7.5 hours, there is also N for nights and E for evenings, which are 10 and 8 hours each. Since there are many names in this rota, what I wanted to do was have the rota with C,N and E in each column but for it to then add up the hours that person has worked over a certain period either a month or a week. I'm sorry if this doesn't make a lot of sense but could anybody steer me in the right direction? I'm guessing I need some sort of macro to search for the C,N and E's but as from there I am clueless.
Thanks everyone