It used to take 54 hours for a factory to manufacture a walking tractor, but now it takes 18 hours less to manufacture one. How many more walk-behind tractors can be built in the time it took to build 90 walk-behind tractors?
某工厂原来制造一台手扶拖拉机要用54小时，现在造一台可少用18小时．用原来造90台手扶拖拉机的时间，现在可以多造多少台手扶拖拉机？
<gadget id="calculator">54 - 18</gadget>
<output>36</output>

<gadget id="calculator">90 / 36</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">54 * (5/2)</gadget>
<output>135</output>

<gadget id="calculator">135 - 90</gadget>
<output>45</output>

<result>45</result>