If my math is right that's about 14 m/gal highway and a little over 9 m/gal city. If both our figures are correct this appears to be about 1/2 what you should expect to be getting. Could be bad engine temp sensor or O2 sensor (if you have one). Or maybe leaking fuel regulator diaphram. Bad knock sensor could retard the timing and I would think maybe cause poor mileage? A really heavy right foot would do it too along with some dragging brake pads. Do the spark plugs look black and sooty from unburned gas.