the average decrease in value can be solve by first solving the value at year 1 and year 2
and i think the equation is f(x)=10,000(0.73)^x
at x = 1
f(x) = 10,000(0.73)^x
f(1) = 10,000(0.73)^(1)
f(1) = 7300
at x = 2
f(x) = 10,000(0.73)^x
f(2) = 10,000(0.73)^(2)
f(2) = 5329
so the average decrease = ( 7300 - 5329) = $ 1971 per year