Answer:
16 hours.
Explanation:
Let x represent number of hours.
We have been given that a moving company charges $800 plus $16 per hour. The total cost of the company moving for x hours would be
.
Another moving company charges $720 plus $21 per hour. The total cost of the company moving for x hours would be
.
Now, we will equate both expression to solve for x.
![21x+720=16x+800](https://img.qammunity.org/2020/formulas/mathematics/middle-school/w6a2bewu1hk030odmzvtqltskpr98sv5d4.png)
![21x-16x+720=16x-16x+800](https://img.qammunity.org/2020/formulas/mathematics/middle-school/1bu4r1kol4dfwpxkt4ne5a0e50dalrbutk.png)
![5x+720=800](https://img.qammunity.org/2020/formulas/mathematics/middle-school/b1zh9odssdb91kwfe8own3zn7llq6mu426.png)
![5x+720-720=800-720](https://img.qammunity.org/2020/formulas/mathematics/middle-school/hwdpt9aip4nz352ng68fru7hjqgpcl00y7.png)
![5x=80](https://img.qammunity.org/2020/formulas/mathematics/middle-school/1hc4dg65queqk5dp4phb9yg71eo69wv910.png)
![(5x)/(5)=(80)/(5)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/21x42se9zcxs3c7opbrdo4s1985dm9rrjg.png)
![x=16](https://img.qammunity.org/2020/formulas/mathematics/high-school/54vswjfry49nj26yghmmk853abj0561j72.png)
Therefore, at 16 hours the amount charged by both companies will be same.