In one hour, Bart fixes 6 flat tires.
In one hour, Art fixes 16/3 flat tires.
In one hour both working together fix:
[tex]6+\frac{16}{3}=\frac{34}{3}[/tex]34/3 tires in one hour.
This means that to fix 68 flat tires, they will need:
[tex]\frac{68}{\frac{34}{3}}=68\cdot\frac{3}{34}=6[/tex]Answer: 6 hours
