If one shirt takes 1 hour to dry in the sun, then 3 shirts would also take 1 hour to dry, assuming:

1. You have enough space to lay all 3 shirts out in the sun simultaneously
2. Each shirt receives adequate sunlight exposure
3. The environmental conditions (temperature, humidity, sunlight intensity) remain the same

The drying time doesn't increase with more shirts because each shirt dries independently when properly exposed to the sun. This is different from sequential processes where you'd have to dry one shirt after another.