Write the proportion equations and solve [[$ x $]].

a) The ratio of [[$ 40 $]] to [[$ 5 $]] is equal to the ratio of [[$ x $]] to [[$ 10 $]].



[[$ x = $]]

b) The ratio of [[$ 100 $]] to [[$ x $]] is equal to the ratio of [[$ 4 $]] to [[$ 5 $]].



[[$ x = $]]