The country A Consumer Price Index is approximated by the following​ formula, where t represents the number of years after 1990.
a(t)=100e^0.023t
For​ instance, since​ A(16) is about 144​, the amount of goods that could be purchased for​ $100 in 1990 cost about ​$144 in 2006. Use the function to determine the year during which costs will be 90​% higher than in 1990.