Assume that the Pure Expectation Theory determines interest rates in the markets. Today's market rates for different maturities follow an interesting pattern. The spot rate for investing for 1 year is 4%. After that, the rate increases by 1% for each year. So, in general, the rate for year Y is simply 4% + 1%*(Y-1).

Given this information, what is the implied interest rate to invest for 1 year, starting in 4 years?

Enter your answer as a percentage, rounded to 1 decimal, and omitting the '%' sign. For example, if your answer is 0.0123456, this is equivalent to 1.23456%, so just enter 1.2

(the correct answer is 12.1 - please show me how to do this step by step- excel formulas are welcomed)- thank you!