Answer
$\mathscr{E} = 56.8~V$
Work Step by Step
In part (a), we found that $A = h^2$, where $h$ is the height of the bar above the vertex.
We can find the magnitude of the emf:
$\mathscr{E} = \frac{d\Phi}{dt}$
$\mathscr{E} = B~\frac{dA}{dt}$
$\mathscr{E} = B~\frac{dA}{dh}~\frac{dh}{dt}$
$\mathscr{E} = B~2h~v$
$\mathscr{E} = (2)(0.350~T)(15.6~m)(5.20~m/s)$
$\mathscr{E} = 56.8~V$