Answer
$6.78\frac{m}{s}$
Work Step by Step
According to law of conservation of energy
$K.E_{bottom}+U_{bottom}=K.E_{top}+U_{top}$
$\implies \frac{1}{2}mv_{bottom}^2+0=\frac{1}{2}mv_{top}^2+mgy_{top}$
This can be rearranged as:
$v_{bottom}=\sqrt{v_{top}^2+2gy_{top}}$
We plug in the known values to obtain:
$v_{bottom}=\sqrt{(0.840)^2+2(9.81)(2.31)}$
$v_{bottom}=6.78\frac{m}{s}$