Answer:
6
Explanation:
To find the mean, we take the numbers on the cards and divide by the number of cards. Let x be the number on the 5th card
( 3+5+7+9+x) / 5 = 6
(24+x)/5 = 6
Multiply both sides by 5
24+x = 30
Subtract 24 from each side
24+x-23 = 30-24
x=6