Adding numbers up

Hi,
I have a file with three columns, one is date, the other is source of income and the third one is amount of money. What I would like to do is to have in one cell total amount of money that comes from 3 specific sources of income (in column b there are about 7-8 different sources of income). Is this possible? I don't want to every time use the filter to choose sources of income, i would like to always be able to see what the total is of those specific sources of income.

Thanks for the pointer, I will look into how this formulas work

I got it to work with sumifs function, thanks!