Earth is described by the equation: x + y + z = -18

Mars is described by the equation: 4x + 3y − z = −3

Venus is described by the equation: 3x + 3y + z = 4

Find all the points that Earth, Mars and Venus have in common using:

a/ Solving the respective system of linear equations using "Gaussian Elimination" with "Back Substitution"

b/ Solving the respective system of linear equation in matrix form AX=B by calculating the determinant and inverse of A.