Jak cut the grass in 6 hours thus in 1 hour he will cut 1/6 of the grass

Ana can do it in 7 hours this in 1 hour she will cut 1/7 of the grass

let 'x' represent the number of hours needed to cut the grass together, x>0

In 1 hour Jak and Anna will cut 1/x of the grass

Now we have:

1/6 + 1/7 = 1/x

by solving we find:

x = 42/13 hr

x = 3 3/13 hr

x = 3 hr 3*60/13 min

x = 3 hr 14 min approximately

click here to see the step by step solution of the equation:

it will take them 3 hours and 14 minutes the cut the grass together.