John is preparing for a marathon and decides to do a training session consisting of running and biking. He bikes 30 miles at a speed of \(4x\) miles per hour, then switches to running and runs 10 miles at a speed of \(x\) miles per hour. If the total time spent on biking and running is 3 hours and 30 minutes, find his running speed \(x\) in miles per hour. (You may use a calculator on this problem.) Let's think step by step and output the final answer within \boxed{}.
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