What conditions on b 1 , b 2 , b 3 , b 4 make each system solvable? Solve for x:    1 2 2 4 2 5 3 9    " x 1 x 2 # =    b 1 b 2 b 3 b 4       1 2 3 2 4 6 2 5 7 3 9 12       x 1 x 2 x 3    =    b 1 b 2 b 3 b 4  