quetion name Tricks

Hi my dear tutor, I have a question

Direct labor

semi-skilled–100 hours @ $ 3.50————$350

Note 4

Semi-skilled labor is presently under-utilised, and 200 hours per week are currently recorded as idle time. if the printing work is carried out, 25 unskilled hours would have to occur during the weekend, but the employees concerned would be given two hours time off druing the week in lieu of each hour worked at the weekend.

underutilised 100 hours

idle time——-200
weekend—-(75)
job
equal———-125
remaining—–(25)
weekends
equal————100
time off—- —-(50)
surplus equal–50

its relevant cost is zero.I know idle time will be paid anyway therefore its relevant cost is zero.
My question here is that could you explain the above solution method and I watched it lsbf video when the tutor explained it but i could not catch it but i know that its relevant cost is zero

thanks in advance