i believe these answers for (a) & (b)(ii) are not correct.

for (a), the question states that the 4 balls are taken WITH REPLACEMENT. this means that number of balls remains the same. the answer posted on left, is assuming the case of 4 balls taken without replacement.

(b)(ii) answer is incorrect due to error carried forward from (a).

answers given by EPQP in comments in main section should be the correct answers.