<h2>A can complete the work in 7*6 hrs = 42 hrs.
</h2><h2>
</h2><h2>A can complete in 1 hr = 1/42 part.
</h2><h2>
</h2><h2>B can complete the work in 7*8 hr = 56 hrs.
</h2><h2>
</h2><h2>A&B together do in 1 hr = 1/42 + 1/56 = 7/168 = 1/24 part. So they will do in 8 hrs = 8*1/24 = 1/3 part.
</h2><h2>
</h2><h2>Hence they need 1÷1/3 = 3 days to complete the work.</h2>
