After one year its value is (100-12)% of what it was at the start of the year

(100-12)%=88%=88/100=0.88

So you can find 88% of $10,000 by doing 0.88x10,000

and 88% of that is 0.88 x your answer

and 88% of that is 0.88 x your answer.

To do it in one quick easy calculation work out 0.88^3 x 10000