Its simple math, doesn’t matter what number you choose at first, multiplying it by 2 and then adding 5 and multiplying again by 50 will get rid of it’s impact from the final age calculation.
After you do those 3 steps you’ll end up with a number starting from 350,450 .. up to 1150, notice that final two digits are always 50 (this is how the effect of the staring number is taken out).
And then we are asked to add 1758 or 1759, again if you forget first two parts of the number (17); that means add 58 or 59 to 50, which will give you either 08 or 09. Notice that 09 is almost like 2009 (for the last two digits) Now they ask to subtract your birth year (for example lets take 1985, that’s not by birth year if anyone is wondering..

) from that , so in essence its like subtracting 85 from 08 or 09, get the pattern ?