Need help solving with detail

Question

Bob can paint a fence in 4 hours.

Sue can paint the same fence in 3 hours.

How long will it take them to paint the fence if they work together?

Answer 1

For these type of work problems you set it up as follows

1/4 + 1/3 = 1/x

Get a common denominator (12x) to get

3x/12x + 4x/12x = 12/12x

You can cancel out the denominators (actually multiply both sides by 12x) to get

3x + 4x = 12

7x = 12

x = 12/7 = 1 5/7 hrs