Answer:
The answer is 1/6.
Explanation:
The question is worded in such a way to be open to misunderstanding. I feel it could mean Norah must spread her stone at the rate of 2/3 of a ton per square yard across 4 square yards and the total is sought.
It could also be saying that Norah has 2/3 of a ton to be divided equally across 4 square yards and is seeking the amount of stone each square yard needs.
In the former case it is a matter of multiplying the vulgar fraction by four and in the latter case the answer could be approached by considering the total amount of stone given is four times the answer that is required and so would be given by dividing 2/3 by 4/1 or more simply by multiplying by 1/4 and not forgetting to cancel the resulting fraction down to the lowest common denominator.
A better way for practical purposes would be to convert 2/3 of a ton into pounds and then divide by four. A workman required to do the work would not be messing around with fractions but would be working in pounds and tons or if using Imperial measure it would be pounds, stones, hundredweight and tons.