\(B=\left(1+\dfrac{2}{3}-\dfrac{1}{4}\right).\left(\dfrac{4}{5}-\dfrac{3}{4}\right)^2:\dfrac{17}{4800}\)
\(=\left(\dfrac{12}{12}+\dfrac{8}{12}-\dfrac{3}{12}\right).\left(\dfrac{16}{20}-\dfrac{15}{20}\right)^2.\dfrac{4800}{17}\)
\(=\dfrac{17}{12}.\left(\dfrac{1}{20}\right)^2.\dfrac{4800}{17}\)
\(=\dfrac{17}{12}.\dfrac{1}{400}.\dfrac{4800}{17}\)
\(=1\)
\(B=\left(1+\dfrac{2}{3}-\dfrac{1}{4}\right).\left(\dfrac{4}{5}-\dfrac{3}{4}\right)^2:\dfrac{17}{4800}\\ =\dfrac{17}{12}.\dfrac{1}{400}:\dfrac{17}{4800}\\ =\dfrac{17}{4800}:\dfrac{17}{4800}\\ =1\)