Is there anyone that can solve this for me and tell me how they came up with the answer? ? (pic included)

Plz heeeeeeelp plz give me the answer

Graph red beads cost $1 an ounce and gold beads cost $3 an ounce. juanita wants to purchase a 12-ounce mixture of red and gold beads that she can sell for $2 an ounce. the solution of the system shows the number of beads needed for juanita to break even. x + y = 12, x + 3y = 24 how many ounces of red beads will juanita buy to break even? how many ounces of gold beads will she buy?

What is the value of x in the equation (2)3) (x+6)= -18 a. -36 b. -33 c. -24 d. -18