Answer:
![F=0.41w](https://img.qammunity.org/2020/formulas/mathematics/middle-school/v4bv08h1q8pltodvszk1tde5wd4c0ny7a5.png)
Explanation:
1. You know that the force F varies directly as the weight w of the sofa. Then, you can write the following expression:
![F=kw](https://img.qammunity.org/2020/formulas/mathematics/middle-school/cr13mdkex6gfdmdoupuuo63jnxlu9fzk38.png)
Where k is the constant of proportionality.
2. You know that a person can push a 120 pound sofa with a force of 50 pounds, then you can calcualte the constant of proportionality as following:
![k=(F)/(w)=(50lb)/(120lb)=0.41](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8mwwqbr2b5t26cgs3l6d6divvrpk00jpja.png)
3. Then, the equation is:
![F=0.41w](https://img.qammunity.org/2020/formulas/mathematics/middle-school/v4bv08h1q8pltodvszk1tde5wd4c0ny7a5.png)