MU divided by price yields:

a) taco MU/$4: 6.75,5.75,4.75,3.75,2.75
b) soda MU/$2: 5.5,4.5,3.5,2.5,1.5,.5
c) Another patron offers you a 3rd & 4th soda for the last taco you ordered, you give away utils and get utils and hence refuse/prefer to trade.
d) No change in utils as tacos and sodas have different marginal utilities.