I think the answer is if you multiply. 10m X 20w= 200, now if you devide 39.37 in 200 is equal to 5.08in
300.50 (assuming the first x means multiplication )
40,000
All you do is multiply 4,000 by 10 to find out what 10 times of your number is, if 4,000 is only 1/10 of it.
This can be expressed by,
80 + 40 + 20 + 10 = 150