If this is a True or False question, that is true.
Easy, showing work,
using the method FOIL (First,Outer,Inner, Last)
Take, (x+3)(x+5) and multiply,
First,
x*x=

Outer,
x*5=5x
Inner,
3*x=3x
Last,
3*5=15
Add the terms together,

+8x+15 (

+5x+3x+15)
Thus, your answer.
The constant is "4.5 miles per hour", or whatever the actual units are.