That's a HM Treasury inflation analysis finding that a sterling depreciation after Brexit would cost the typical family £120 a year by 2018 -- based on estimation of the above equation. If it's a choice between equations and Hitler references, the typical family might just take Hitler references.
More seriously, the cost is all based on an assumption that Sterling would depreciate by 12 percent after Brexit. Thus, if sterling would go to up by 12 percent, families would be better off by the same amount. Treble appreciations all round!