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 7 seconds than it was moving after 5 seconds?
Choose the correct choice from the following answers:
A) 4
B) 28
C) 15
D) 48
E) 63
Given: z=s^2+2s for 0≤s≤7   z(5) = 5^2 + 2*5 = 35   z(7) = 7^2 + 2*7 = 63   Therefore z(7) - z(3) = 63 - 35= 
<gadget id="calculator">63 - 35</gadget>
<output>28</output>
28 km/hr   Option 28
<result>B</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 7 seconds than it was moving after 5 seconds?