Xiao Ming has 90 pictures, and Xiao Qiang has 60 pictures. If Xiao Ming has four times as many pictures as Xiao Qiang, how many stamps must Xiao Qiang give to Xiao Ming?
小明有图片90张，小强有图片60张，要使小明的图片张数是小强的4倍，那么小强必须给小明多少张邮票？
<gadget id="calculator">60 + 90</gadget>
<output>150</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">150 / 5</gadget>
<output>30</output>

<gadget id="calculator">60 - 30</gadget>
<output>30</output>

<result>30</result>