3. These three equations have a common solution. Solve the first two x+y=3, x-y= 1 to get x=2, y= 1, and substitute x-2my = o to get m= 1.

4. Multiply two sides of (1) 3x-y =12x-4y = 4, and add two sides of 5x+4y=2 to get 17x = 6,, x = 6/ 17. Similarly, in the equation,