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.