The school brigade department bought a batch of pencil cases as prizes, and distributed them to 15 classes on average, with 6 in each class, and there were 21 left. How many pencil boxes did the school brigade buy in total?
学校大队部买来一批文具盒作奖品，平均发给15个班，每班6个，还剩下21个，学校大队部一共买来多少个文具盒？
<gadget id="calculator">6 * 15</gadget>
<output>90</output>

<gadget id="calculator">90 + 21</gadget>
<output>111</output>

<result>111</result>