Final answer:
Layla must spend 3 days on vacation to buy a total of 18 postcards, calculated by dividing the total postcards desired by the number of postcards she buys per day.
Step-by-step explanation:
To calculate how many days Layla must spend on vacation to buy a total of 18 postcards, we should use division. Layla buys 6 postcards each day, so we divide the total postcards she wants to buy (18 postcards) by the number of postcards she buys per day (6 postcards/day).
The calculation is: 18 postcards ÷ 6 postcards/day = 3 days.
Therefore, Layla has to spend 3 days on vacation to buy a total of 18 postcards.