Solve using augmented matrix methods. 4x1 - x2 = 5 12X7 3x3 = - 15 Select the correct choice below and, if necessary, fill in the answer box to complete your choice. and X2 O A. The unique solution is x, = (Simplify your answer.) The system has infinitely many solutions. The solution is X1 . and x2 = (Simplify your answer. Type an expression using t as the variable) O C. There is no solution