Solve this problem using a rule of three
1 stick ------------------------ 10 cents
64 stickers ------------------ x
x = (64 x 10) / 1
x = 640 / 1
x = 640 cents
Lia needs to pay 640 cents
1 dollar ----------------- 100 cents
x ---------------- 640 cents
x = (640 x 1) / 100
x = 640/100
x = 6.4 dollars
Lia needs to pay $6.4 dollars