In 1960, the oldest of three brothers has an age that is the sum of the of his younger siblings. A few years later, the sum of the ages of two of brothers is double that of the other. A number of years have now passed since 1960, which is equal to two thirds of the sum of the ages that the three brothers were at that year, and one of them has reached 21 years. What is the age of each of the others two? algebranumber theorysystem of equations