Answer: The variable cost per unit of manufacturing product X is $3.
Explanation: If manufacturing 50 units costs $ 200.
And manufacturing 80 units costs $ 290.
The variable cost of manufacturing (80 - 50 = 30) 30 more units is ($ 290 - $ 200 = $ 90) $ 90.
If we divide the variable cost over the units (90/30 = $ 3) We know that the variable cost of producing a unit of product X is $ 3.