It would appear that who ever gave you that problem thinks that you know what those things mean! Do you? Have you written the coefficient matrix and augmented matrix for the system?
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.