Acarpenter can do a job in four hours. his assistant can do the same job in six hours. how long would it take them to do the job together?

if the carpenter can do the whole job in 4 hours, that means in 1 hour, it has only done 1/4 of the whole thing.

if his assistant can do the job in 6 hours, that means, in 1 hour, he has done only 1/6 of the whole job.

let's say if both of them work together, they can do the job in "t" hours, so in 1 hour alone, the carpenter has done 1/4 of it, and the assistant has done 1/6 of it, for a total of 1/t of the job.