An equation for that would be.
x => 67
If the first gardener can finish the job in 6 hours, it means that every hour he completes 1/6 of the job.
By the same logic, the second gardener completes 1/7 of the job per hour.
So, if they work together, they complete

of the job per hour.
So, after 42/13 of a hour, they'll complete the job. Since one hour is made of 60 minutes, 42/13 of a hour is

So, it will take them about 194 minutes to finish the job, i.e. about 3 hours and 14 minutes.
All you have to do is multiply 18.3 x 5.1
18.3×5.1=93.33
It will take 93.33 minutes to repair the entire section. Hope that helps!
I think it's D as an answer but I could be wrong