If we assume that the given cost of iPhone 6s (gray cell) is cell O114, then the cells around it get filled with formulas that calculate what the column header tells you.
Cell P114 is the ratio of this year's CPI to last year's, so will have the formula ...
=N114/N113
Cell Q114 is the annual inflation rate. You can express this different ways, but the usual way is as a percentage. A percentage change is calculated as ...
((new value) -(old value))/(old value) × 100%
This can be rearranged to ...
((new value)/(old value) -1) × 100%
Of course, the ratio (new value)/(old value) is the one in column P, so the formula for cell Q114 is simply ...
=P114-1
with the cell formatting is set to <em>show the value as a percent</em>.
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The cell phone costs that go in column O can make use of the ratio calculated in column P, or they can be formulated using the CPI directly. Either way, the previous year's cell phone cost is the current year's cost divided by the ratio in column P. That is, cell O113 could be either of ...
=O114/P114
=O114/N114*N113
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Of course, once you put these formulas in the cells at the bottom of the table, you must fill them upward so they calculate values for previous years. The attachment shows a recreation of a small part of your table, with the formula bar showing the formula in the highlighted cell.
