Fuel consumption

I have a 89 plymouth reliant miles: 103500 4 cylinder. I just bought this car and from the spot it had been sitting in for the last year with no gas in it, I put 10 dollars in it to drive it to my house, and the 3 1/2 gallons I put in I only made it 37 miles and the 3 1/2 gallons were gone, theres no fuel leak from what I can see, and no real smell of gas. So what could be my next few steps to fix this problem in a affortable way? And when I checked what the m.P.G. Should be it says 25-31 mpg, im barely getting 10 miles to the gallon. Please help!