Its been awhile since I took a math class, I was reviewing this question but I do not understand where the $\displaystyle 4 $came from. I understand the rest but I am clueless about that$\displaystyle 4$

$\displaystyle 4000=1000$ x $\displaystyle (1+r)^5$

$\displaystyle (1+r)^5=4$

$\displaystyle (1+r)=4.0$^(1/5)$\displaystyle =1.32$

$\displaystyle r=.32$

This came from my math book.