Budgeted total cost for the next period question

Here’s the question

114) budgeted production in a factory for next period is 4800 units. Each unit requires five Labour hours to make. Labour is paid $10 per hour. Idle time represents 20% of the total Labour time.

Okay so my question is, why do you divide my 0.8 and not multiply by 1.2 (I.e increase time taken by 20% to cover the 20% idle time)

I’m still stuck after watching lectures.

Kind regards,