Answer
The period of the 3.0-m long pendulum is 3.67 seconds.
Work Step by Step
Let $T$ be the period of a pendulum and let $L$ be the length of a pendulum. Therefore;
$T \propto \sqrt{L}$
$T_1 \propto \sqrt{L_1}$
$T_2 \propto \sqrt{L_2}$
We can use the ratio of $\frac{T_2}{T_1}$ to find $T_2$.
$\frac{T_2}{T_1} = \frac{\sqrt{L_2}}{\sqrt{L_1}}$
$T_2 = T_1~\frac{\sqrt{L_2}}{\sqrt{L_1}}$
$T_2 = (3.0~s)~\frac{\sqrt{3.0~m}}{\sqrt{2.0~m}}$
$T_2 = 3.67~s$
The period of the 3.0-m long pendulum is 3.67 seconds.
