The students collected tree seeds. The third grade collected 45 kilograms, and the fourth grade collected three times that of the third grade. How many kilograms were collected in the fourth grade than in the third grade? (calculated using two arithmetic methods)
同学们采集树种子，三年级采集了45千克，四年级采集的是三年级的3倍，四年级比三年级多采集多少千克？(用两种算术方法计算)
<gadget id="calculator">45 * 3</gadget>
<output>135</output>

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

<result>90</result>