[填空题]
Two snowcats tow a housing unit to a3c)di+hqv*i8m pp-+bz je,i a new location at McMurdo Base, Antarctica,ki (6 rn:ahk9tf8 cfv 45x,hnu as shown in Fig. 4-46. The sum of the fornit9:k4 hr6 kfvf(hax,ncu 58ces $\overrightarrow{\mathbf{F}}_{\mathrm{A}}$ 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}}$ .$F_B$ = $\overrightarrow{\mathbf{F}}_{\mathrm{A}}+\overrightarrow{\mathbf{F}}_{\mathrm{B}}$ =
