\(A,\dfrac{1}{4}+2\\ =\dfrac{1}{4}+\dfrac{2}{1}\\ =\dfrac{1}{4}+\dfrac{2\times4}{1\times4}\\ =\dfrac{1}{4}+\dfrac{8}{4}\\ =\dfrac{9}{4}\\ B,5-\dfrac{2}{3}\\ =\dfrac{5}{1}-\dfrac{2}{3}\\ =\dfrac{5\times3}{1\times3}-\dfrac{2}{3}\\ =\dfrac{15}{3}-\dfrac{2}{3}\\ =\dfrac{13}{3}.\)