The shop sells 66 yellow balloons, and sells 42 red balloons three times less than the yellow balloons. How many red balloons were sold?
商店卖出66个黄气球，卖出的红气球比黄气球的3倍少42个．卖出多少个红气球？
<gadget id="calculator">66 * 3</gadget>
<output>198</output>

<gadget id="calculator">198 - 42</gadget>
<output>156</output>

<result>156</result>