It Only Hurts When I Think About It

I have just performed my weekly painful duty. It becomes more painful when expressed in the following formula:

(3.75*a)* b = c
c*(d/3.75) = ouch

where:
a = price per liter of gasoline in euros (€)
b = current exchange rate US$ to €
c = price per gallon of gasoline in dollars
d = liters to fill tank at station
ouch = cost in dollars to fill tank

The price per liter continues to go up and the value of the dollar against the euro continues to fall, meaning that each euro spent represents more dollars. When I saw the latest price hike at the station, I decided to see what that comes to in dollars/gallon, at the current dollar rate. The final value of c was $7.48/gallon for 98 octane.

So when I fill up now, I go for the cheap gas (95 octane). It's a bargain at $6.80 a gallon, and this week I filled up for under $70... $69.61 (Ouch)