Subtract the product of 13.5 and 6 from 291, divide the difference by 4.2, what is the quotient?
291减去13.5与6的积，所得的差除以4.2，商是多少．
<gadget id="calculator">13.5 * 6</gadget>
<output>81</output>

<gadget id="calculator">291 - 81</gadget>
<output>210</output>

<gadget id="calculator">210 / 4.2</gadget>
<output>50</output>

<result>50</result>