From the supply chain perspective, Which Part is the bottleneck?

Operation Number of Workers Assigned Operation Time in Minutes 8 8 Frame production 1. Cut tubes and weld small frame parts to the tubes 2. Tack weld front triangle, then permanently weld 3. Attach rear triangle to front triangle 4. Slit and ream seat tube 5. Check frame measurements 1 8 1 6 7 Painting 1. Acid wash 32* 2. Apply base paint coat by robot 3. Apply 1-3 finish coats 4** 7 + 40 mins dry time. No workers are required for drying. 16 mins/coat + 40 mins/coat dry time. No workers are required for drying 1 8 4. Stencil name Assembly and boxing 11** 88