$($Problem No$.3\mathrm{.}6,$ page $68)$ A $4-m$ long rigid body carrying a $10-k\frac{N}{m}$ uniformly distributed load is supported by a pinned connection and cable as shown in the attached figure. How much is the reaction at $B(R_{BY})?$

A$.0kN$

B$.10kN$

C$.20kN$

D$.40kN$