Answer:
Length is 20 in
Height is 4 in
Explanation:
we are given
The width of a rectangular box is 8in
so,
![W=8](https://img.qammunity.org/2020/formulas/mathematics/middle-school/fuv43f3jnbxvk5qihce9neubinuu0z9gp6.png)
The height is one fifth the length
Let's assume length =x
L=x
![H=(1)/(5)x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/fg03d8g09bdhnpymhtbp1pwocdl1hndgv2.png)
now, we can find volume
![V=L* W* H](https://img.qammunity.org/2020/formulas/mathematics/middle-school/zajxyhlt5bmjf12zbdokplpi3mkpi7vro0.png)
we can plug
![640=x* 8* (1)/(5)x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/w3p2rj9wduwcdwxthsgmg8dwu8cswp266v.png)
now, we can solve for x
![(8)/(5)x^2=640](https://img.qammunity.org/2020/formulas/mathematics/middle-school/2at72dypkm0c9d9fvl2cmko8pu98uawmka.png)
![x^2=400](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ei8gdg3ur1z49nnt8cy4x0lvytdtkk0m8a.png)
![x=20](https://img.qammunity.org/2020/formulas/mathematics/high-school/lncuy5yedis5fwvw5ht2vne9yrrdelw3dm.png)
so, L=20 in
![H=(1)/(5)* 20](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8dktz5bp95rpwbu17qjy8hflusk5mcy65i.png)
![H=4](https://img.qammunity.org/2020/formulas/mathematics/middle-school/fjdlyhbe1j47udkxa563jmzcd54miwrms6.png)
So,
Length is 20 in
Height is 4 in