[tex]d=rt\\\\a.\\\\rt=d\qquad|\text{divide both sides by} r\neq0\\\\t=\dfrac{d}{r}\\\\b.\\d=300\ miles,\ r=60\ mph.\ \text{Substitute}\\\\t=\dfrac{300}{60}h=50h\\\\c.\\rt=d\qquad|\text{divide both sides by}\ t\neq0\\\\r=\dfrac{d}{t}\\\\d=250\ miles,\ t=4.5\ h.\ \text{Substitute}\\\\r=\dfrac{250}{4.5}mph=\dfrac{2500}{45}mph=55\dfrac{25}{45}mph=55\dfrac{5}{9}mph\approx55.6mph[/tex]
