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	$0.80	$0.50
	Every additional 10 g or part thereof	$0.40

How much did Gwen pay for the postage when she sent a letter which weighed 71 g and 9 postcards to Thailand by airmail?
Remaining mass that Gwen had to pay for the letter as it was more than 40 g
= 71 - 40
= 31 g

Number of sets of additional 10 g of the letter that Gwen had to pay for 
= 31 ÷ 10
= 3 r 1

Total number of sets of additional 10 g of the letter that Gwen had to pay for 
= 3 + 1
= 4

Amount that Gwen had to pay for the sets of additional 10 g of the letter
= 4 x 0.40
= $1.60

Total amount that Gwen had to pay for the letter
= 0.80 + 1.60
= $2.40

Amount that Gwen had to pay for the 9 postcards
= 9 x 0.50
= $4.50

Total amount that Gwen paid
= 2.40 + 4.50
= $6.90

Answer(s): $6.90