Xiao Ming participates in the riddle guessing competition, and has to guess 15 riddles in total. It is stipulated that every correct guess will get 10 points, and every wrong guess will deduct 5 points. Xiao Ming finally scored 90 points, how many did he guess correctly?
小明参加猜谜语比赛，共要猜15个谜语，规定每猜对1个得10分，猜错1个扣5分，不猜的按猜错计．小明最后得了90分，他猜对了多少个？
<gadget id="calculator">10 * 15</gadget>
<output>150</output>

<gadget id="calculator">150 - 90</gadget>
<output>60</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<gadget id="calculator">60 / 15</gadget>
<output>4</output>

<gadget id="calculator">15 - 4</gadget>
<output>11</output>

<result>11</result>