November 8th, 2022
Two mountain bikers started from the ranger station in Rocky Mountain National Park traveling in the same direction on Trail Ridge Road. The first biker left 1 hour earlier than the second and traveled 10 miles/hour. The second biker left later and traveled 15 miles/hour. By 4:00 pm, the second biker had passed the first and was 5 miles ahead of the first biker. What time did the first biker leave the ranger station?
Please show how you arrived at the answer.