Two ships, A and B, are traveling towards each other from two places at the same time. A travels 20km per hour, while B travels 28km per hour. When they meet, B travels 84km longer than A. How many hours did they meet? (Solve first with equations, then with arithmetic)
甲乙两船同时从两地相向而行，甲每时行20km，乙船每时行28km，相遇时，乙船比甲船多行84km．它们经过多少小时相遇？(先用方程解，再用算术方法解)
<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<gadget id="calculator">84 / 8</gadget>
<output>21/2 = around 10.5</output>

<result>21/2 = around 10.5</result>