Here's a nice way of doing it:

For each of the three fruits, we could have a banana, a cherry, or a pineapple. So this gives us 3 * 3 * 3 = 27 options. But we can't have three cherries, so remove that possibility. 27 - 1 = 26. Done!

How many different patterns or how many patterns altogether, including duplicates?

Well if we assume the patterns are all different, then I agree that there are 26 combinations.

However, GMat questions teach us never to assume, so perhaps we should consider the other possibility. In fact as there are 4 bananas available to use, it may be a hint not to make this assumption. Just because the fruit are identical doesn't mean that 2 or more patterns can't look identical. For example, if a pair of dice each had 2 fives and 4 threes, we could not ignore the duplicates in our count, when calculating our odds - even if they were identical.

9 * 8 * 7 * 6 = 3024 patterns including 3024 - 26 = 2998 repeats.

From the answers offered, I can only now deduce that the patterns must be distinctly different.

Therefore the answer is 26 (answer b)

Not being pedantic. Just exercising ideas