If the ages of Joe and Andy are added to thrice the age of Mary, the total becomes 79. If the ages of Joe and Mary are added to twice the age of Andy, the total becomes 61 and if the age of Mary is added to thrice the age of Andy and thrice the age of Joe, the total becomes 101. What is the age of Mary?
1
16 yrs
2
12 yrs
3
17 yrs
4
15 yrs
5
18 yrs