The speed of a subway train is represented by the equation z=s^2+2s for all situations where 0≤s≤7, where z is the rate of speed in kilometers per hour and s is the time in seconds from the moment the train starts moving. In kilometers per hour, how much faster is the subway train moving after 6 seconds than it was moving after 3 seconds? Pick one.
A) 4
B) 9
C) 15
D) 48
E) 33
Given: z=s^2+2s for 0≤s≤7   z(3) = 3^2 + 2*3 = 15   z(6) = 6^2 + 2*6 = 48   Therefore z(7) - z(3) = 48 - 15= 
<gadget id="calculator">48 - 15</gadget>
<output>33</output>
33 km/hr   Option 33
<result>E</result>
The speed of a subway train is represented by the equation z=s^2+2s for all situations where 0≤s≤7, where z is the rate of speed in kilometers per hour and s is the time in seconds from the moment the train starts moving. In kilometers per hour, how much faster is the subway train moving after 6 seconds than it was moving after 3 seconds?