Let "△" be a new operation rule, such as 2△3=2+3+4=9, 5△4=5+6+7+8=26, ..., according to this rule 7△4=how much.
设"△"是新的运算规则，如2△3=2+3+4=9，5△4=5+6+7+8=26，…，按此规则7△4=多少．
<gadget id="calculator">7 + 8 + 9 + 10</gadget>
<output>34</output>

<result>34</result>