The document describes a system of linear equations in matrix form. There are 4 equations (A1=, A2=, A3=, A4=) with 4 unknowns (X1, X2, X3, X4). The coefficients of the equations are provided in a 4x4 matrix and the constant terms are provided in a column vector. The document also shows the steps to solve the system of equations using matrix multiplication and inversion to obtain the solutions for the unknowns X1, X2, X3, X4.