81 Students aren't sure what they are going to be doing.
First, find the number of students for each category by multiplying the percentage:
450 x .68 = 306 (306 students want to go to college)
450 x .14 = 63 (63 students are going to begin working)
Add 306 + 63 students to get 369 total students who know what they want to do.
Subtract this number from 450 students total (450-369) to get 81 students who are unsure of what they will do after graduating.