A surveyor determines that the horizontal distance from 'A' to 'B' is 400m, and the horizontal distance from 'A' to 'C' is 500m. Graphically determine the magnitude of the vector ( {BF} ). a) ( lvert {BF} rvert = √{400² + 500²} ) b) ( lvert {BF} rvert = 100 ) units. c) ( lvert {BF} rvert = 300 ) units. d) ( lvert {BF} rvert = 200 ) units.