Aman made lake is stocked with 10,000 fish. this population is expected to decline by an annual rate of 15%. predict the fish population 5 years after the lake is stocked

I got 2,500 left after 5 years.
10,000*15% = 1,500 or you could do 10,000*.15 = 1,500

That is a loss of 1,500 fish per year.
If you want to think of this as a proportion then you would do
Year/fish lost

1/1,500 = 5/x
X=5*1,500
X=7,500

The population of the fish after 5 years equals
10,000-7,500 = 2,500
So your answer is 2,500 fish are left