Those who landed at Skagway made their way over the White Pass before cutting across to Bennett Lake. Although the trail began gently, it progressed over several mountains with paths as narrow as 2 feet  and in wider parts covered with boulders and sharp rocks. Under these conditions horses died in huge numbers, giving the route the informal name of Dead Horse Trail. The volumes of travellers and the wet weather made the trail impassable and, by late 1897, it was closed until further notice, leaving around 5,000 stranded in Skagway. An alternative toll road suitable for wagons was eventually constructed and this, combined with colder weather that froze the muddy ground, allowed the White Pass to reopen, and prospectors began to make their way into Canada. Moving supplies and equipment over the pass had to be done in stages. Most divided their belongings into 65 pounds  packages that could be carried on a man's back, or heavier loads that could be pulled by hand on a sled. Ferrying packages forwards and walking back for more, a prospector would need about thirty round trips, a distance of at least 2,500 miles , before they had moved all of their supplies to the end of the trail. Even using a heavy sled, a strong man would be covering 1,000 miles  and need around 90 days to reach Lake Bennett.
Question: How many round trips did prospectors need for ferrying packages?
Answer: 30