Answer:
36
Explanation:
What you can do is figure it out each side at a time then put the information together:
In a 6 by 9 RECTANGLE, a 3 by 3 SQUARE, can go in twice horizontally, and three times vertically, so 2 x 3 = 6
Since the side facing us is 3 as well, it goes into 18 six times or 6 x 6 = 36