Revision of MA Test your understanding 3

I was going through the revision and i stuck on the question:

The fastest time in which a batch of 20 ‘spicy meat special’ sandwiches
has been made was 32 minutes, with no hold-ups. However, work
studies have shown that, on average, about 8% of the sandwich makers’
time is non-productive and that, in addition to this, setup time (getting
ingredients together etc.), is 2 minutes.
If the sandwich-makers are paid $4.50 per hour, what is the
attainable standard labour cost of one sandwich?

I don’t know how to work out the Non-productive idle time.
any help?

Thanks