On Sunday, Dad and Xiao Ming are going to grandma’s house. Dad just went out and found that Xiao Ming is 15 meters ahead. Dad immediately catches up. Dad’s steps are big. He takes 5 steps and Xiao Ming takes 8 steps. But Xiao Ming moves quickly, and Xiao Ming can walk 4 steps in the time his father takes 3 steps. How many meters must Dad walk to catch up with Xiao Ming?
星期天，爸爸和小明要到外婆家，爸爸刚刚出门发现小明已经在前方15米处，爸爸立即追上去，爸爸步子大，他走5步的路程小明要走8步．但是小明动作快，爸爸走3步的时间，小明却能走4步．爸爸至少走出多少米才能追上小明？
<gadget id="calculator">3 * 8</gadget>
<output>24</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">24 - 20</gadget>
<output>4</output>

<gadget id="calculator">15 / 4</gadget>
<output>15/4 = around 3.75</output>

<gadget id="calculator">24 * (15/4)</gadget>
<output>90</output>

<result>90</result>