As the interest owed per $100 is $10, then, for $400 would be:
[tex]\frac{x}{400}=\frac{10}{100}[/tex][tex]x=\frac{10}{100}\cdot400[/tex][tex]x=40[/tex]Then, at the end of the 5 weeks you will owe the borrowed quantity plus the interest.
[tex]400+40=440[/tex]Answer: $440