Tom plants 10 trees a year.  Every year he also chops down 2 trees a year.  He starts with 50 trees.  After 10 years 30% of the trees die.  How many trees does he have left?
He gets 10-2=
<gadget id="calculator">10-2</gadget>
<output>8</output>
8 new trees a year.
After 10 years he has 8*10=
<gadget id="calculator">8*10</gadget>
<output>80</output>
80 new trees.
So he had 80+50=
<gadget id="calculator">80+50</gadget>
<output>130</output>
130 trees.
He lost 130*.3=
<gadget id="calculator">130*.3</gadget>
<output>39</output>
39 trees.
That means he had 130-39=
<gadget id="calculator">130-39</gadget>
<output>91</output>
91 trees.

<result>91</result>