Need help with Units of Production Depreciation method please! Thank You!

Suppose the Atlanta Falcons purchased a new set of goal posts for $20,000 each. The Falcons expect the goal posts to have a useful life of five years and a salvage value of $1,000 each when they sell them to a local high school. Suppose the team depreciates the asset based on number of goals scored. The team anticipates goals to be 40 in the first year, 46 in the second year, 38 in the third, 50 in the fourth when they win the Super Bowl, and 45 in the fifth year. Compute their first year depreciation using the units-of-production method. Please explain how you arrived at your answer and show work step by step. Thank You