Since fraction given is 2/9, we make things easy to calculate by letting tingfeng's be 9 units at first.

2/9 is as good as saying 2 units out of 9 units.

Aisha gets 2 units. Neighbour gets the same. Also 2 units.

Stamps tingfeng has left
= 9 units - 2 units - 2 units
= 5 units.

Aisha has same number of stamps as him now. She also has 5 units.


Their total = 10 units.


Now if Aisha gives 66 to tingfeng, he would have 4 times as much as her.

This means she has 1/5 of their total and tingfeng has 4/5 of their total.

So Aisha's stamps after that
= 1/5 x 10 units
= 2 units

(Or 10 units ÷ 5 = 2 units)

Units she gave to tingfeng

= 5 units - 2 units
= 3 units

3 units = 66 stamps

1 unit = 66 stamps ÷ 3 = 22 stamps


Stamps they had altogether at first
= Their total now + 2 units the neighbour got from tingfeng

= 10 units + 2 units
= 12 units

12 x 22 stamps

= 264 stamps



b)

Aisha's stamps at first
= Their total at first - tingfeng's at first
= 12 units - 9 units
= 3 units



Total they paid for the stamps at first

= 3 units x $0.15 + 9 units x $0.20

= 3 x 22 x $0.15 + 9 x 22 $0.20

= $49.50

Thank you for the detailed steps :)

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