12. Suppose memory or size restrictions prevent your matrix program from working with matrices having more than 32 rows and 32 columns and suppose some project involves 50x50 matrices A and B (a) (5 points) Solve Ax b for some vector b in IR50 assuming that A can be partitioned into a 2x2 block matrix Aij, with Au an invertible 20 x 20 matrix, A22 an invertible 30 x 30 matrix, and A12 a zero matrix. Hint: Describe appropriate smaller systems to solve, without using any matrix 1Tl inverse