Select the equation needed to solve the following word problem:
Kayla is sending invitations to 20 of her friends for a pizza party. If there are 12 invitations left to send out, how many invitations has she already mailed?
A. [tex]x + 12 = 20[/tex] B. [tex]x + 20 = 12[/tex] C. [tex]x - 8 = 20[/tex] D. [tex]x + 8 = 12[/tex]