406
First, add the digits other than the units, 330 + 60 = 390. Remember that for a moment. Now, add the one's digits, 8 + 8 = 16. Now, add the 16 to the 390 to get 406. ---- Alternately, subtract two from 68 and give it to 338, so we have 340 + 60 + 6 = 400 + 6 = 406