Two trucks with a self-weight of 3000 kg, each equipped with 3 machine tools, and each machine tool weighs 2 tons. Is it safe to pass a bridge with a weight limit of 20 tons at the same time?
两辆自重均为3000千克的卡车，每辆车上都装有3台机床，每台机床重2吨，要同时通过一座限重20吨的桥，是否安全？
<result>20</result>