Throughput Accounting

Question – After manufacture, each heater has to go through three processes:
‘Assembly’, ‘Quality Control’ and ‘Packaging’. The following
information is available for the three heaters:
Alpha Beta Gamma
Sales price per unit $2.00 $2.25 $1.75
Direct materials cost per unit $0.50 $0.81 $0.35
Direct labour cost per unit $0.30 $0.60 $0.50
Machine time per unit:
Assembly (in minutes) 2 3 2.5
Quality Control (in minutes) 3 4 2
Pa After manufacture, each heater has to go through three processes:
‘Assembly’, ‘Quality Control’ and ‘Packaging’. The following
information is available for the three heaters:
Alpha Beta Gamma
Sales price per unit $2.00 $2.25 $1.75
Direct materials cost per unit $0.50 $0.81 $0.35
Direct labour cost per unit $0.30 $0.60 $0.50
Machine time per unit:
Assembly (in minutes) 2 3 2.5
Quality Control (in minutes) 3 4 2
Packaging (in minutes) 4 5 3
Weekly sales demand 1,000 units 1,500 units 850 units

Operating expenses, including labour, are $4,000. The maximum
hours available for the machines are 150 hours (Assembly), 170
hours (Quality Control) and 250 hours (Packaging).

As per the answer : The ‘Assembly’ hours needed for maximum production are 143.75.
This is less than the 150 hours available. The ‘Quality Control’ hours
needed for maximum production are 178.33, which is greater than
the 170 hours available. So, ‘quality control hours’ is the limiting
resource/bottleneck. The ‘Packaging’ hours needed for maximum
production are 234.17. This is less than the 250 hours available.

My Question is how did they calculated this max production like 143.75?