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

Destination	Letters		Postcards
	Mass	Postage Rate	Per piece
New Zealand, Australia	1st 20 g	$1.40	$0.50
	Every additional 10 g or part thereof	$0.20

How much did Penelope pay for the postage when she sent a letter which weighed 89 g and 7 postcards to New Zealand by airmail?
Remaining mass that Penelope had to pay for the letter as it was more than 20 g
= 89 - 20
= 69 g

Number of sets of additional 10 g of the letter that Penelope had to pay for 
= 69 ÷ 10
= 6 r 9

Total number of sets of additional 10 g of the letter that Penelope had to pay for 
= 6 + 1
= 7

Amount that Penelope had to pay for the sets of additional 10 g of the letter
= 7 x 0.20
= $1.40

Total amount that Penelope had to pay for the letter
= 1.40 + 1.40
= $2.80

Amount that Penelope had to pay for the 7 postcards
= 7 x 0.50
= $3.50

Total amount that Penelope paid
= 2.80 + 3.50
= $6.30

Answer(s): $6.30