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.Answersx+y=21,3x+4y=68x+y=68, 3x+4y=21x+y=21, 4x+3y=68x+y=68, 4x+3y=21