Answer
The magnitude of the charge on the block is $1.45\times 10^{-5}~C$ and the sign is negative.
Work Step by Step
The electric force directed up the plane is equal in magnitude to the component of the block's weight directed down the plane. We can find the magnitude of the charge $q$ on the block:
$E~q = mg~sin~\theta$
$q = \frac{mg~sin~\theta}{E}$
$q = \frac{(0.00235~kg)(9.80~m/s^2)~sin~17.0^{\circ}}{465~N/C}$
$q = 1.45\times 10^{-5}~C$
Since the electric force is directed up the plane, the charge on the block must be negative. The magnitude of the charge on the block is $1.45\times 10^{-5}~C$ and the sign is negative.
