Answer
4 $\times$ $10^{4}$
Work Step by Step
You have f(x)=5000 $\times$ $2^{x}$.Where it represents the investment after x decades.Plug in x=3 since 30 years is 3 decades:
f(3)=5000 $\times$ $2^{3}$
f(3)=40000
Put it into scientific notation form :4 $\times$ $10^{4}$
