Which device is used to convert digital data into analog data and then back into digital data in order to send the data through a phone line?

Use a software program or a graphing utility with matrix capabilities to solve the system of linear equations using an inverse matrix. x1 + 2x2 − x3 + 3x4 − x5 = 6 x1 − 3x2 + x3 + 2x4 − x5 = −6 2x1 + x2 + x3 − 3x4 + x5 = 3 x1 − x2 + 2x3 + x4 − x5 = −3 2x1 + x2 − x3 + 2x4 + x5 = 5