$$\require{cancel} $$ $$50 \times\frac{miles}{hour} = 50 \times\frac{miles}{60 minutes}=\frac{5}{6}\times\frac{miles}{minute}$$ $$\Rightarrow120\ miles\div(\frac{5}{6}\times\frac{miles}{minute})=120\ \cancel{miles}\times(\frac{6}{5}\times\frac{minute}{\cancel{miles}})=144\ minutes$$