The numbers of the pump indicate that the fuel cost 67.9 cents per gallon and a total cost of $19.00. The price of gasoline in 1981 was around $1.30 per gallon; the old pumps were not capable of charging more than 99.9 cents, so they were set to half the price and it was then doubled. That is why the teenager asks for $38.00.
There are windows on the landing of the stairway up to the second floor. When Chelsea and her new boyfriend the dentist and the dentist's son arrive it's dark outside. But sunshine is coming through the windows on the landing. Whereas all other windows are showing dark. And the time is verified that it is dark outside when Chelsea comes into the house and greets her father.