How many exercises should i do per muscle when i do a four day split?

[billy]

I plan on doing an exercise routine for a four day split to gain size. i plan on doing 3 sets of each exercise with a rep range from 5-8 and my split is going to be: day one - chest and tri's, day two back and bi's, day three shoulders, day four legs. but i don't know how many exercises to do for each muscle. Any workout routine or exercises too would be helpful.