Answer
oversleeping $60$, computer problems $70$, illness $140$.
Work Step by Step
Step 1. Assume the number involving oversleeping is $x$; then the number involving computer problems is $x+10$ and the number involving illness is $x+80$.
Step 2. Combining the above three excuses, we have $x+x+10+x+80=270$, or $3x=180$ and $x=60$.
Step 3. Thus, the number due to oversleeping is $60$, due to computer problems is $70$, and for illness it is $140$.
