Kristin spent $131 on shirts. fancy shirts cost $28 and plain shirts cost $15. if she bought a total of 7 then how many of each kind did she buy

Hi there!!

First, Let plain shirts be x
Let fancy shirts be y 
x + y = 7
15x + 28y = 131 
Multiply first equation by 28 to eliminate y: 
28x + 28y = 196
15x + 28y = 131 
Subtracting the two equations:
13x = 65
x = 5 
Substituting x to get y:
x + y = 7
5 + y = 7
y = 2 
5 plain shirts and 2 fancy shirts

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