Since 20 students are interested in teaching only, they are a group onto themselves (they are independent) 

This means that 319 students are interested in comp science and finance.

183 + 194 = 377 students total (too many, we are only dealing with 319) so there are some students who are interested in both. 377 - 319 = 58 

58 students are interested in both com sci and finance. I'll subtract these from the totals...

183 - 58 = 125 in comp. sci. only

194 - 58 = 136 in finance only

As a check, 125 + 136 +58 = 319 + 20 = 339