Let the shoe size be X and the year of birth be1900+Y.

So this value is

(2x+39)X50+56- 1900-y = 100 x+ 1950+56- 1900-y = 100 x+ 106-y

So the first two digits are the shoe size, and the last two digits are 106 minus the year of birth. So it can be solved. Of course, this is a problem in 2006, and it is true.