How can I find a margin of error when the only information given is the 90% confidence interval numbers?

Question

On my statistics homework, I have to find the margin of error given only the following:

"The results of a recent World Health Organization (WHO) study stated that a 90% confidence interval on the annual cost of rabies in Asia and Africa was $540 - $626 (in millions)"

Everything I've seen online requires either a standard deviation or a sample size, which I am not given either of.

Answer 1

The CI is equal to mean - margin of error, mean + margin of error, so margin of error is half the width of the confidence interval. 626M - 540M / 2 = 43 M.

Answer 2

So one thing we should know is that the mean is in the middle of the lower and upper bounds. So 540+626/2=583. So 583 would be our sample mean. So then we also know that the z score is 1.645. So far,

we have 583 +/- 1.96*sd/sqrt(n). So knowing this, the margin of error is 43. Here is your answer.