A grandfather has three grandsons, the eldest grandson is 24 years old, the second grandson is 18 years old, and the youngest grandson is 15 years old. 15 years later, the sum of the ages of the three grandchildren is 70 years less than twice the age of the grandfather, so how old is the grandfather this year?
一位老爷爷有三个孙子，今年大孙子24岁，二孙子18岁，小孙子15岁．15年后，这三个孙子的年龄和比爷爷年龄的2倍少70岁，那么爷爷今年多少岁？
<result>71</result>