[填空题]
Two snowcats tow a hou+ sql(urcqb1 ym07hn *sin udgamu0 kh .b4sj g6;p.f;vx*g unit to a new location at McMurdo Base, Antarctica, as shown in Fig. 4-46. The sum of the gxgk*u muf;dhb.4v. p;a j0 6sforces $\overrightarrow{\mathbf{F}}_{\mathrm{A}}$ and $\overrightarrow{\mathbf{F}}_{\mathrm{B}} $ exerted on the unit by the horizontal cables is parallel to the line L , and $ F_{\mathrm{A}}=4500 \mathrm{~N} $. Determine $ F_{\mathrm{B}}$ and the magnitude of $ \overrightarrow{\mathbf{F}}_{\mathrm{A}}+\overrightarrow{\mathbf{F}}_{\mathrm{B}}$ .$F_B$ = $\overrightarrow{\mathbf{F}}_{\mathrm{A}}+\overrightarrow{\mathbf{F}}_{\mathrm{B}}$ =
