a. $-2+\dfrac45+\dfrac56 =\dfrac{-2\times30}{30}+\dfrac{4\times6}{5\times6}+\dfrac{5\times5}{6\times5}$
$=\dfrac{-60+24+25}{30} =-\dfrac{11}{30}$.

b. $\dfrac12+\dfrac23+\dfrac34 =\dfrac{1\times6}{2\times6}+\dfrac{2\times4}{3\times4}+\dfrac{3\times3}{4\times3} =\dfrac{6+8+9}{12}$
$=\dfrac{23}{12}$.

c. $-2+\dfrac18-\dfrac5{16} =\dfrac{-2\times16}{16}+\dfrac{1\times2}{8\times2}-\dfrac{5}{16} =\dfrac{-32+2-5}{16}$
$=-\dfrac{35}{16}$.

d. $\dfrac5{16}-\dfrac7{24}+1 =\dfrac{5\times3}{16\times3} - \dfrac{7\times2}{24\times2}+\dfrac{48}{48} =\dfrac{15-14+48}{48}$
$=\dfrac{49}{48}$.