Tim and Rick both can run at speed v_r and walk at speed v_w, with v_{\rm r} v_{\rm w}. They set off together on a journey of distance D. Rick...

Tim and Rick both can run at speed v_r and walk at speed v_w, with v_{rm r} > v_{rm w}. They set off together on a journey of distance D. Rick walks half of the distance and runs the other half. Tim walks half of the time and runs the other half.How long does it take Rick to cover the distance D?Find Rick's average speed for covering the distance D.