Robots Robert and Hubert assemble and disassemble coffee grinders. Each of them assembles a coffee grinder four times faster than they can disassemble it. When they came to the workshop in the morning, several coffee grinders were already assembled there.

At 7:00, Hubert started assembling and Robert started disassembling, and precisely at 12:00, Hubert finished assembling a coffee grinder and Robert finished disassembling another one. In total, 70 coffee grinders were added during this shift.

At 13:00, Robert started assembling and Hubert started disassembling, and precisely at 22:00, Robert finished assembling the last coffee grinder and Hubert finished disassembling another one. In total, 36 coffee grinders were added during this shift.

How long would it take to assemble 360 coffee grinders if Robert and Hubert were assembling together? (K. Pazourek)

Hint. How many coffee grinders will be added per hour in each shift?