Matrices cap A and cap b shown are equal. cap A is equal to the 2 by 2 matrix, row 1, column 1, 7 column 2, negative 18 row 2, column 1, 3 column 2, 24 cap b is equal to the 2 by 2 matrix, row 1, column 1, b sub 11 column 2, b sub 12 row 2, column 1, b sub 21 column 2, b sub 22 What is the value of b sub 12 ?