The answer seems to be 108
He was 51 years old. He was 33 when he first started exploring. Then 17 years later he explored again so you add 17 +33 =50 . Then 11 years later he died so you add 11 to 50 =51
Estimation :
20/0.05 = 400
5y + 7 < = -3
5y < = -3 - 7
5y < = -10
y < = -10/5
y < = -2
3y - 2 > = 13
3y > = 13 + 2
3y > = 15
y > = 15/3
y > = 5
