Add: [74865167]+[86123660]\displaystyle {\left[\begin{array}{cccc} -{7}&{4}&-{8}&-{6}\\-{5}&{1}&{6}&{7}\end{array}\right]}+{\left[\begin{array}{cccc} -{8}&{6}&{1}&{2}\\-{3}&{6}&-{6}&{0}\end{array}\right]}