The fifth grade students of Nanzha Primary School planted 45 trees, the number of trees planted by the fourth grade students was 18 times less than that of the fifth grade students, how many trees were planted by the fourth grade students.
南栅小学五年级同学植树45棵，四年级同学植树的棵数比五年级的2倍少18棵，四年级同学植树多少棵．
<gadget id="calculator">45 * 2</gadget>
<output>90</output>

<gadget id="calculator">90 - 18</gadget>
<output>72</output>

<result>72</result>