The graph shows the relationship between the total cost and the number of gift cards that raj bought for raffle prizes.

a graph titled cost of gift cards. the x-axis shows the number of gift cards, numbered 1 to 9, and the y-axis shows the total cost in dollars, numbered 10 to 90. blue diamonds appear at points (1, 20), (2, 40), (3, 60), (4, 80).
what would be the cost for 5 of the gift cards?

for each new desk that is purchased, by how much does the amount of money left in the school’s desk fund decrease?