What was the difference in the Discount based on incremental borrowing rate between Charter-in vessels in operation and Land Leases? 
{"December 31, 2020": {"Charter-in vessels in operation": 109574, "Land Leases": 556, "Office space": 753}, "December 31, 2021": {"Charter-in vessels in operation": 85399, "Land Leases": 556, "Office space": 356}, "December 31, 2022": {"Charter-in vessels in operation": 57282, "Land Leases": 556, "Office space": 101}, "December 31, 2023": {"Charter-in vessels in operation": 47603, "Land Leases": 556, "Office space": 81}, "December 31, 2024": {"Charter-in vessels in operation": 34025, "Land Leases": 556, "Office space": "\u2014"}, "December 31, 2025 and thereafter": {"Charter-in vessels in operation": 33481, "Land Leases": 23002, "Office space": "\u2014"}, "Total": {"Charter-in vessels in operation": 367364, "Land Leases": 25782, "Office space": 1291}, "Operating lease liabilities, including current portion": {"Charter-in vessels in operation": 304568, "Land Leases": 7660, "Office space": 1204}, "Discount based on incremental borrowing rate": {"Charter-in vessels in operation": 62796, "Land Leases": 18122, "Office space": 87}}
incremental_borrowing_rate_charterin_vessels_in_operation = df["Discount based on incremental borrowing rate"]["Charter-in vessels in operation"]
incremental_borrowing_rate_land_leases = df["Discount based on incremental borrowing rate"]["Land Leases"]
answer = incremental_borrowing_rate_charterin_vessels_in_operation - incremental_borrowing_rate_land_leases