Kara has 21 collectible buttons to sell. she sells the small buttons for $3 and the large buttons for $4, and earns a total of $68. if the small buttons are represented by x and the large buttons are represented by y which of the following systems of equations can be used to calculate the number of large and small buttons sold.
answers
x+y=21,3x+4y=68
x+y=68, 3x+4y=21
x+y=21, 4x+3y=68
x+y=68, 4x+3y=21

Can someone i have no idea of how to do this.

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