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

Destination	Letters		Postcards
	Mass	Postage Rate	Per piece
Indonesia, Malaysia	1st 20 g	$1.50	$0.80
	Every additional 10 g or part thereof	$0.40

How much did Erika pay for the postage when she sent a letter which weighed 89 g and 7 postcards to Indonesia by airmail?
Remaining mass that Erika 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 Erika had to pay for 
= 69 ÷ 10
= 6 r 9

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

Amount that Erika had to pay for the sets of additional 10 g of the letter
= 7 x 0.40
= $2.80

Total amount that Erika had to pay for the letter
= 1.50 + 2.80
= $4.30

Amount that Erika had to pay for the 7 postcards
= 7 x 0.80
= $5.60

Total amount that Erika paid
= 4.30 + 5.60
= $9.90

Answer(s): $9.90