Key Question If the CPI was 110 last year and is 121 this year, what is this

Question:

Key Question If the CPI was 110 last year and is 121 this year, what is this year’s rate of inflation? What is the “rule of 70”? How long would it take for the price level to double if inflation persisted at
(a) 2,
(b) 5, and
(c) 10 percent per year?