Answer:
Large box:
![18.5\ kilograms](https://img.qammunity.org/2020/formulas/mathematics/middle-school/wvg5ajx52kkjb939a1rxew3n06wb84o9c2.png)
Small box:
![15.25\ kilograms](https://img.qammunity.org/2020/formulas/mathematics/middle-school/7hrlq2sdbc1zfj4fcjllbxpih2y49o28iv.png)
Explanation:
Let be "l" the weight in kilograms of a large box and "s" the weight in kilograms of a smalll box.
Set up a system of equations:
![\left \{ {{3l+2s=86} \atop {8l+4s=209}} \right.](https://img.qammunity.org/2020/formulas/mathematics/middle-school/rozvwy0unmtrxcqcbruesvz0s618ba3u8h.png)
In order to solve the system of equations, you can apply the Elimination Method. Multiply the first equation by -2, add the equations and then solve for "l":
![\left \{ {{-6l-4s=-172} \atop {8l+4s=209}} \right.\\......................\\2l=37\\\\l=(37)/(2)\\\\l=18.5](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8s4jirs5wpe9r62hr9cqhok02ajoguryph.png)
Finally, susbstitute the value of "l" into any original equation and solve for "s":
![3(18.5)+2s=86\\\\2s=86-55.5\\\\s=(30.5)/(2)\\\\s=15.25](https://img.qammunity.org/2020/formulas/mathematics/middle-school/r0j583k47vad8yz5rdg4l5ig858xy2f7t6.png)