If you mean what is 600 times 25, there's an easy way to multiply by 25 because 25=100/4. This means we divide by 4 and add two zeroes to the result. 600/4=150, add on the two zeroes and we get 15000.
If you mean what number gives us a difference of 600 times 25 between that number and 25, then we have to add 25 to the number we just found=15025. 15025 less 25 is 600 times 25.