Think your cell number last digit as X and your age as Y then
(X*2+5)*50+Y+365-615
=100X+250+Y-250
=100X+y
X can be 1,2..9
Any number multiply by 100 mean it come as first number with two zero
That's why you get "The last 2 digits as your age and The 1st digit as your cell's last number"...