Answer:
$15
Step-by-step explanation:
Can't help you with the drop down, as we need to know the info for Station A to be able to compare it with Station B, however, the cost for charging a car at Station B for 4 hours is:
use f(x) = 3x + 3 as the value of x = 4 falls in this function's interval
So f(4) = (3 x 4) + 3 = 15
So it will cost $15 for a car to charge for 4 hours at Station B.
