If they are linear equations (no squared terms, no cubics, etc), there are seveal options. If you know how to use matrices, use them; otherwise, if you know how to use determinants, use them. If not, reduce four equations in four unknowns down to three equation in three unknowns.
Example:
3w - 4x + y - 2z = 7
w + 3x - 5y + 7z = -7
2w + 2x + 5y - 2z = 26
4w - 3z + 2y - z = 16
Choose a variable to eliminate from all four equations. If you choose w:
Looking at equations 1 and 2:
3w - 4x + y - 2z = 7 ---> 3w - 4x + y - 2z = 7
w + 3x - 5y + 7z = -7 ---> x -3 ---> -3w - 9x + 15y - 21z = 21
Add down the columns: -13x + 16y - 23 z = 28
Looking at equations 2 and 3:
w + 3x - 5y + 7z = -7 ---> x -2 ---> -2w - 6x +10y - 14z = 14
2w + 2x + 5y - 2z = 26 ---> 2w + 2x + 5y - 2z = 26
Add down the columns: -4x + 15y - 16z = 40
Looking at equations 2 and 4:
w + 3x - 5y + 7z = -7 ---> x -4 ---> -4w - 12x + 20y - 28z = 28
4w - 3z + 2y - z = 16 ---> 4w - 3z + 2y - z = 16
Add down the columns: -15w + 22y - 29z = 44
Putting these equations together:
-13x + 6y - 23 z = 28
-4x + 15y - 16z = 40
-15w + 22y - 30z = 44
Now you have three equation in three unknowns; can you solve it from here?
