Teacher Wang kept half of the monthly income and 20 yuan as living expenses, and saved half of the remaining money and 50 yuan. At this time, there was 40 yuan left to pay the children's tuition and book fees. How much is his monthly income?
王老师把月收入的一半又20元留做生活费，又把剩余钱的一半又50元储蓄起来，这时还剩40元给孩子交学费书本费．他这个月收入多少元？
<gadget id="calculator">40 + 50</gadget>
<output>90</output>

<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">180 + 20</gadget>
<output>200</output>

<gadget id="calculator">200 * 2</gadget>
<output>400</output>

<result>400</result>