Mario bought $5 worth of stamps at the post office. he bought ten more 6-cent stamps than 10-cent stamps. the number of 8-cent stamps was three times the number of 10-cent stamps. he also bought two 20-cent stamps. how many of each kind of stamp did he purchase?

He bought 2 20-cent stamps.
That is $0.40.
He spent $4.60 on the other stamps.

He bought x 6-cent stamps, y 10-cent stamps, and z 8-cent stamps.

y + 10 = x
z = 3y

6x + 10y + 8z = 460

6(y + 10) + 10y + 8(3y) = 460

6y + 60 + 10y + 24y = 460

40y + 60 = 460

40y = 400

y = 10

x = y + 10 = 10 + 10 = 20

z = 3y = 3(10) = 30

He bought
20 6-cent stamps
10 10-cent stamps
30 8-cent stamps
2 20-cent stamps