2x^2 - 8 = 0
2x^2 = 8
x^2 = 8/2 = 4
x = sqrt(4) = 2 or -2
To find the answer, set up an equation:

Using this set up we can cross out the units that are on opposite sides of the proportion such as miles and hours, leaving us with the desired units of meters and seconds. Then calculate m/s by multiplying 45 by 1000 meters and then dividing that value by 3600 seconds.
The resulting answer is 45mph = 12.5 m/s
It would be 20 percent, I believe. First you would put it into a fraction of 12\60, then you would simplify that into 3\15 then divide as shown. You end up with .2 which would be 20 percent.