I am trying to help a couple of friends w/ horizontals shifts w/ the following data:

Month & Ave temp (oF)
Jan: 21.1
Feb: 26.9
Mar: 38.6
Apr: 51.9
May: 62.4
Jun: 72.1
Jul: 76.9
Aug: 74.1
Sep: 65.1
Oct: 53.4
Nov: 39.0
Dec: 25.1

I need to find the horizontal shift, which i kow can be found using (x_0 = |h|/b), but cannot figure out h, or x_0. Please help.