I will guess that you meant to say the following:

If so, then note that, for Ax = b, you have A^(-1)Ax = A^(-1)b = x. So you need onlyFind the 2 x 2 matrix which maps R back to Q.Code:The matrix [ 1 2 ] [ 1 3 ] maps Q(1, 2) to R(5, 7)]find the matrix inverse.