Hello, diehardmath4!

Crew A can pave a certain length of highway in 9 hours,

while crew B can do the same job in 12 hours.

How long would it take if they worked together?

Crew A can do the job in 9 hours.

. . In one hour, it can do of the job.

. . In hours, it can do of the job.

Crew B can do the job is 12 hours.

. . In one hour, it can do of the job.

. . In hours, it can do of the job.

Working together for hours, they can do: . of the job.

But in hours, we expect them tocompletethe job (1 job).

There is our equation: .

Now solve for . . .