If there are x people assembling a table for two, there will be 9-x people assembling a single chair.

Then 4x= 10(9-x)/2.

The solution is x=5.

Then assign five people to assemble a double table and four people to assemble a single chair.

In the same way; In a similar way

If there are x people assembling a double table, there will be 3 1-x people assembling a single chair.

Then 4x= 10(3 1-x)/2.

X is not an integer.

So you can't assign work.