Explanation:

To solve this question, we can apply a short trick approach;
If M₁ persons can do W₁ work in H₁ hours and M₂ persons can do W₂ work in H₂ hours, then we have formula M₁H₁W₂ = M₂H₂W₁
Given:
M₁ = 1, H₁ = 6, W₁ = 30
M₂ = ?, H₂ = 3, W₂ = 80
Now, as
M₁H₁W₂ = M₂H₂W₁
1 × 6 × 80 = ? × 3 × 30
⇒ ? = 1 × 6 × 80 / 3 x 30 = 16/3 = 5 1/3
we can't have fraction number of computers.
Hence, we can say to complete 80 tasks, there should be 6 computers operating simultaneously.