I would first organize it by putting 2 and 3/8 over 1 hour, and having x points over 4 hours, because we don't know how much points were lost in a duration of 4 hours. You take 2 and 3/8 over 1 and the x over 4 hours and you make them equal each other. You'll understand this when you see my picture. After that you cross multiply them, so 2 and 3/8 multiplied by 4 is 9 and a half, and x multiplied 1 is x. In the end, you would have x = 9 and a half. Substituting now this information for x, we now know that in 4 hours that 9 and a half points were lost, so using this we take 23 and subtract it by 9 and a half to get 13.5.
