Acertain motorcycle manufacturer has been building motorcycles for 98 years. over that period, production has increased steadily at an annual rate of 5%, so that the production rate, in motorcycles/year, after t years was

r(t)=a⋅1.05^t

where a is a constant representing the initial production rate. what fraction of their total production was built during the last 13 years? your answer should be a number between 0 and 1.