Respuesta :
Answer: x+y=21, 3x+4y=68
Explanation:
Here x represents the number of small button and y represents the number of large button,
And, According to the question,
Total number of button = 21
Thus, Â x + y = 21
Also, She sells the small buttons for $3 and the large buttons for $4, and earns a total of $68
That is, Â 3x + 4y = 68
Thus, the system of equations that can be used  to calculate the number of large and small buttons sold are,
x + y = 21, Â 3x + 4y = 68
First Option is correct.