According to the meaning of the question:
x/6+x/ 12+x/7+5+x/2+4=x
To solve this equation:
x=84
The mathematician lived to 84 years old.
You can also use arithmetic:
(5+4)÷( 1- 1/6- 1/ 12- 1/7- 1/2)
=9÷(9/84)
=84 years old
The mathematician lived to 84 years old.