\(\dfrac{30-x}{30}\) = \(\dfrac{5}{15}\)
\(\dfrac{30-x}{30}\) = \(\dfrac{1}{3}\)
30 - \(x\) = \(\dfrac{1}{3}\) \(\times\) 30
30 - \(x\) = 10
\(x\) =30 - 10
\(x\) = 20
\(\dfrac{x+30}{72}\) = \(\dfrac{5}{8}\)
\(x+30\) = \(\dfrac{5}{8}\) \(\times\) 72
\(x+30\) = 45
\(x\) = 45 - 30
\(x\) = 15