For Mr. Wang’s pancakes, you can put up to 3 pancakes in the pot each time. Both sides must be baked, and each side needs to be baked for 3 minutes. Master Wang is going to bake 7 cakes, how long will it take at least?
王师傅烙饼，每次锅里最多能放3张饼，两面都要烙，每面需要烙3分钟．王师傅准备烙7张饼，至少要花多长时间？
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">6 + 9</gadget>
<output>15</output>

<result>15</result>