A small block of mass $m$ and charge $Q$ is placed on an insulated, frictionless, inclined plane of angle $\theta$ as in Figure P23.51. An electric field is applied parallel to the incline. (a) Find an expression for the magnitude of the electric field that enables the block to remain at rest. (b) If $m=$ $5.40 \mathrm{g}, Q=-7.00 \mu \mathrm{C},$ and $\theta=$ $25.0^{\circ},$ determine the magnitude and the direction of the electric field that enables the block to remain at rest on the incline.