find all solutions to the following equations. How do I do this???
x1+2x+x3+x4=7
x1+2x2+2x3-x4=12
2x1+4x2+6x4=4
The real question is, how have you learned to solve problems like these? There are a number of ways of solving such equations, ranging from fairly basic (eliminate variables by subtracting) to very sophisticated (row reduce the augmented matrix). Without more information, we cannot possibly know what woul be appropriate for you.