a, MSC: 35
$\dfrac{-5}{5}=\dfrac{-5.7}{5.7}=\dfrac{-35}{35}$
$\dfrac{8}{7}=\dfrac{8.5}{7.5}=\dfrac{40}{35}$
b, MSC: 30
$3=\dfrac{90}{30}$
$\dfrac{-3}{5}=\dfrac{-3.6}{5.6}=\dfrac{-18}{30}$
$\dfrac{-5}{6}=\dfrac{-5.5}{6.5}=\dfrac{-25}{30}$
c, MSC: 105
$\dfrac{-9}{7}=\dfrac{-9.15}{7.15}=\dfrac{-135}{105}$
$\dfrac{-19}{15}=\dfrac{-19.7}{15.7}=\dfrac{-133}{105}$
$-1=\dfrac{-105}{105}$