working together A and B can finish typing 40 pages = (6/ 50) * 40 = 24/5 mints.

Per unit work done by A and B is individually denoted by 1/A and 1/(A - 4) respectively.

Now Substituting all in the form of an equation,we have

1/A + 1/(A -4) = 5 / 24

We obtain a quadratic equation as ,

5A^2 - 68A + 96 = 0

Solving this equation A = 12 mints. Hence for 80 pages 12 * 2 = 24 mints.

Thank you and have fun in 'GMATLAND' as we ALL ARE having.

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