Answer:
There were 18 exhibits at last year's fair.
Explanation:
This year: 3 per month. There are 12 months per year. So 12 * 3 = 36.
So now we have 36 exhibits this year.
But then the question states that "this year's fair has twice as many as last year's." Knowing this, we have to do the inverse of multiplication, which is division.
36/2 = 18