is 3/9=15/45 porportional

Yes, 3/9 is proportional to 15/45.

To determine if two fractions are proportional, you need to check if the cross products of the fractions are equal.

Cross products of 3/9 and 15/45 would be 3 * 45 = 9 * 15, which is 135 = 135. Since the cross products are equal, the fractions are proportional.