Điền vào ô trống

a) \[\begin{array}{l} \times \begin{array}{*{20}{c}}{\,\,\,\,21}\\{\underline {\,\,\,\,14} }\end{array}\\\,\,\,.......\\\,\,\,\underline {.......} \\\,\,\,.......\end{array}\]

b) \[\begin{array}{l} \times \begin{array}{*{20}{c}}{\,\,\,\,\,52}\\{\underline {\,\,\,\,16} }\end{array}\\\,\,\,.......\\\,\,\,\underline {.......} \\\,\,\,.......\end{array}\]