Linear Algebra Problem: Finding the Solution with Inverse Multiplication

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Homework Statement

The Attempt at a Solution

To get to the stuff in the picture, I subtracted [ 6 -7; -1 -2] from both sides and then multiplied on the left by the inverse of [1 8; -5 -3]

Where'd I go wrong?

 

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wait. just verified that my mental math sucks. found the error.