The nominal GDP in base year 2014 was $40 billion. The nominal GDP in year 2015 with price index 120 was $57.6 billion. The real GDP in 2015 can be calculated as follows :
GDP (real) = GDP (nominal) / price index * 100
GDP (real) = 57.6 / 120 * 100
GDP (real) = $48 billion
The growth rate in real GDP from 2014 to 2015 is 1.2%.
Growth rate = 48 * (100/40) = 1.2%
Therefore the growth rate is 12%