Let us assume that each car needs 4 wheels.
Since we have 3520 wheels, we can assemble at the most (3520/4) i.e. 880 cars in a day.
Now 3520 wheels will need (3520 X 4) nuts (as each wheel needs 4 nuts).
Thus, total nuts required for 880 cars will be 14080 nuts.
However, we have only 14040 nuts available.
Therefore, we would need (14080 - 14040) = 40 additional nuts in order to build a max total of 880 cars in a day.
Since each wheel needs 4 nuts and we are short of 40 nuts, we will not be able to assemble (40/4) i.e. 10 wheels.
And since each car needs 4 wheels therefore we won't be able to assemble (10/4) = 2.5 cars.
We need to round off 2.5 to the next highest integer in this case, since the number of cars cannot be a decimal value.
Thus, we won't be able to assemble 3 cars in total.
Thus, in a day we can at max assemble (880 - 3) = 877 cars.
Based on the above explanation we can see that the nuts are the limiting factors in this case.
If you get to put only 850 cars in the day, then your productivity percentage is
(850/877) * 100 = 96.92 %