Sarah Montague speaks to the economist, Professor Sir Paul Collier. The refugee crisis is one of the world's most intractable problems: 60 million people have fled their homes, with a third of them also fleeing their own country. But Professor Collier believes the problem is fixable and "we can do it easily". The solution he argues is to give refugees jobs. In doing so he suggests everyone will benefit. But if the answer was so simple why has it not been done before?