There is a dead simple way to understand percentages.
Percentages are hundredths, so you use them as a two digit number after the decimal point, so 0.25 is 25%.
(OK, 100% is 1.00)
To add 20%, you multiply by 1.20 to give you the original number (100%) plus 20%.
To get 18% of a value, multiply by 0.18
Doing it like this, to reverse any calculation, you divide by the value you originally multiplied by...
If 700,000 was a reduction of 39%, it is 61% of the original value (100 - 39 = 61).
So, by the method above, one way of working it out would have been to multiply the original number by 0.61
To reverse it, divide by 0.61
700,000 / 0.61 = 1147541 to the nearest integer.
1,147,541 in a neater format.
Cross-checking using conventional % on a calculator confirms this.