I think "How is the economy doing" is a better translation for this. Asking how the economy is going makes it sound like the person being asked the question is creating or running/managing the economy.
A literal translation actually works pretty well. "How goes the xxx?" is a valid (if informal) way of asking how something is doing.
"How goes the economy?" was marked wrong, although it sounds a bit more natural that the suggested translation.
Down the pan?