The correct answer is option 4: "Are you saying that in 10 years the city's tax income will be 70 percent less than this year?"
In this option, the meaning of the statement is preserved. The amount of years that will take for the change to be made is the same: ten years. The percentage of the shrink in the city's tax income, which is 70%, is the same as in the statement; also, the idea of the gradual change from this point in time until those ten years have passed is also preserved. Thus the meaning of the whole statement is not distorted as in the other options.