Recovering the simple-interest rate

Statement

A principal of $1800\ \text{€}$ lent for $2$ years yields $216\ \text{€}$ of simple interest. What is the annual rate?

Solution

From $I=C\,r\,t$ we get $r=\dfrac{I}{C\,t}$. $r=\frac{216}{1800\cdot 2}=\frac{216}{3600}=0{.}06=\boxed{6\%}.$