Number of special cards each person had at first = 2 x 40 = 80

Number of normal cards each person had at first = 7 x 40 = 280

Total number of cards each person had at first
= 80 + 280
= 360

3 normal cards were traded for 1 special card.

For every 3 normal cards Weihua traded away, he would receive 1 special card.

3 - 1 = 2

He would have 2 fewer cards than before.

Likewise, for every special card he traded away, he would receive 3 normal cards.

He would have 2 more cards than before.

384 in the end - 360 at first = 24

From this we can see that he has more cards than at first. So he must have traded special cards away and received normal cards.

Since he has 2 more cards than before when he trades away one special card,

24 ÷ 2 = 12

He traded 12 special cards away.

Number of special cards Weihua had in the end = 80 - 12 = 68

i think a is 348.... idk

Alternatively, since you already calculated the number of cards John had in the end in part a), which is 336,

360 - 336 = 24

He had 24 fewer cards than at first. This means he must have traded normal cards away for special cards

Each time he traded 3 normal cards away he received 1 special card. He would have 2 fewer cards than before.

24 ÷ 2 = 12

This tells us he did this 12 times.

He received 12 special cards and traded away 12 x 3 = 36 normal cards.

So Weihua must have traded 12 special cards away.

Thank you for the clear explanation!!