To find the cost of labor for one worker, you multiply the wage by the number of hours worked.
40 * 8 = 320
Because there are two workers, now you double it.
320 * 2 = 640
To find the percentage of the revenue that this is, you do the labor cost divided by the revenue.
640 / 2000 = 0.32
Move the decimal two places to the right to get the percentage.
0.32 = 32%
The labor cost is 32% of the revenue.