The table shows the airmail rates for sending letters and postcards to some countries.

Destination	Letters		Postcards
	Mass	Postage Rate	Per piece
Thailand, Vietnam, Myanmar	1st 40 g	$0.90	$0.50
	Every additional 10 g or part thereof	$0.30

How much did Kathy pay for the postage when she sent a letter which weighed 64 g and 3 postcards to Vietnam by airmail?
Remaining mass that Kathy had to pay for the letter as it was more than 40 g
= 64 - 40
= 24 g

Number of sets of additional 10 g of the letter that Kathy had to pay for 
= 24 ÷ 10
= 2 r 4

Total number of sets of additional 10 g of the letter that Kathy had to pay for 
= 2 + 1
= 3

Amount that Kathy had to pay for the sets of additional 10 g of the letter
= 3 x 0.30
= $0.90

Total amount that Kathy had to pay for the letter
= 0.90 + 0.90
= $1.80

Amount that Kathy had to pay for the 3 postcards
= 3 x 0.50
= $1.50

Total amount that Kathy paid
= 1.80 + 1.50
= $3.30

Answer(s): $3.30