An american football field has $100$ yards + each ends is $10$ yards, for a total of $120$ yards $\dots$ a kicker kicks the balls $105$ yards( he starts at the $35$ yard line at the other end) so he kicked it $70$ yards, the runner runs it back for $23$ yards, which places him on the $18^{th}$ yard line $(105 - 23 = 82 ) $
What formula can I come up with to make sure each play I can accurately get the correct placement of the ball ( in this case the $18^{th}$ yard line )