Two people start running from the same place and direction at the same time on the circular track. It takes 15 minutes for A to run a lap, and 21 minutes for B to run a lap. At least a few minutes later, they meet again at the starting point?
两人在环形跑道上从同一地点同方向同时起跑，甲跑一圈要15分钟，乙跑一圈要21分钟，至少几分钟后他们又在起跑点相遇？
<gadget id="calculator">3 * 5 * 7</gadget>
<output>105</output>

<result>105</result>