[tex]\bf \stackrel{distance}{d}=\stackrel{rate}{r}\cdot \stackrel{time}{t}\qquad \qquad 2\frac{1}{4}m=3\frac{3}{4}\frac{m}{hr}\cdot t\implies \cfrac{2\frac{1}{4}m}{3\frac{3}{4}\frac{m}{hr}}=t
\\\\\\
\cfrac{\frac{9}{4}m}{\frac{15}{4}\frac{m}{hr}}=t\implies \cfrac{9\underline{m}}{4}\cdot \cfrac{4hr}{15\underline{m}}=t\implies \cfrac{9\cdot 4}{4\cdot 15}hr=t\implies \cfrac{3}{5}hr=t[/tex]
so, 36 minutes then.
