Pulling a loaded sled at 10 mph for 180 miles takes 180/10=<<180/10=18>>18 hours
Pulling an unloaded sled at 20 mph for 120 miles takes 120/20=<<120/20=6>>6 hours
Pulling a loaded sled at 10 mph for 80 miles takes 80/10=<<80/10=8>>8 hours
Pulling an unloaded sled at 20 mph for 140 miles takes 140/20=<<140/20=7>>7 hours
In total, Toby will have pulled the sled for 18+6+8+7=<<18+6+8+7=39>>39 hours
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