Answer: the cost of one cherry pie is $18 and the cost of one pumpkin pie is $20
Explanation:
Let x represent the cost of one cherry pie.
Let y represent the cost of one pumpkin pie.
Lea sold 2 cherry pies and 4 pumpkin pies for a total of $116. This means that
2x + 4y = 116 - - - - - - - - - - - - - -1
Kali sold 7 cherry pies and 8 pumpkins pies for a total of $286. This means that
7x + 8y = 286 - - - - - - - - - - - - 2
Multiplying equation 1 by 7 and equation 2 by 2, it becomes
14x + 28y = 812
14x + 16y = 572
Subtracting, it becomes
12y = 240
y = 240/12 = 20
Substituting y = 20 into equation 1, it becomes
2x + 4 × 20 = 116
2x + 80 = 116
2x = 116 - 80 = 36
x = 36/2 = 18