First of all, we know that Emily travels 3/4 of a mile in 4 minutes and 30 seconds (i.e. 9/2 of a minute). So, her current velocity is
[tex]v = \dfrac{\frac{3}{4}}{\frac{9}{2}} =\dfrac{3}{4}\cdot\dfrac{2}{9} = \dfrac{1}{6}[/tex] of a mile per minute.
At this speed, it takes
[tex]t = \dfrac{s}{v} = \dfrac{3.42}{\frac{1}{6}} = 3.42\cdot 6 = 20.52[/tex]
minutes to travel 3.42 miles.
Since she left at 8.25, she will arrive at about 8.46, so she's on time for school.
