Each of them need to work 105 minutes more in order to have packed the same number of boxes.
<u><em>Explanation</em></u>
Suppose, they need to work for
minutes more in order to have packed the same number of boxes.
Selma packs one box in 5 minutes and Trudy packs one box in 7 minutes.
So, the number of boxes packed by Selma in that
minutes
and the number of boxes packed by Trudy in
minutes ![=\frac{x}{7}](https://tex.z-dn.net/?f=%3D%5Cfrac%7Bx%7D%7B7%7D)
Given that, Selma and Trudy have already packed 12 and 18 boxes.
Now if <u>each of them packed the same number of boxes</u>, then the equation will be......
![12+\frac{x}{5}=18+\frac{x}{7}\\ \\ \frac{x}{5}-\frac{x}{7}= 18-12\\ \\ \frac{7x-5x}{35}=6\\ \\ \frac{2x}{35}=6\\ \\ 2x= 210\\ \\ x= \frac{210}{2}=105](https://tex.z-dn.net/?f=12%2B%5Cfrac%7Bx%7D%7B5%7D%3D18%2B%5Cfrac%7Bx%7D%7B7%7D%5C%5C%20%5C%5C%20%5Cfrac%7Bx%7D%7B5%7D-%5Cfrac%7Bx%7D%7B7%7D%3D%2018-12%5C%5C%20%5C%5C%20%5Cfrac%7B7x-5x%7D%7B35%7D%3D6%5C%5C%20%5C%5C%20%5Cfrac%7B2x%7D%7B35%7D%3D6%5C%5C%20%5C%5C%202x%3D%20210%5C%5C%20%5C%5C%20x%3D%20%5Cfrac%7B210%7D%7B2%7D%3D105)
So, each of them need to work 105 minutes more in order to have packed the same number of boxes.