It takes Evan 6 3/4 hours to mow 3 lawns .It takes him 2 1/3 hours to mow

It takes him  hours to mow the third lawn

Explanation:

We are given that Evan takes  hours to mow Mr. Gals lawn and  hours to mow Mrs. Lee's lawn

This means that:

Time taken to mow the two lawns =  hours

Now, we are given that the time taken to mow the three lawns is  hours

This means that:

Time taken to mow the third lawn =  hours

Hope this helps :)