Since there are 8500 chairs
Since this number id decreases by 6%
Then to find 6% of 8500, multiply 6% by 8500
At first, change 6% to a normal number by dividing it by 100
6% = 6/100

The amount of decreases in the number of chairs produced each month is 510
To find the new number of chairs subtract 510 from 8500

The new number of chairs produced each month is 7990