Peppers Lockdown produces keys for homes and cars. As Peppers planned for next year’s production, the company decided to implement a high-low system to forecast future costs. With total production of 2,500,000 keys at a total cost of $10,000 in 2018, and total production of 3,000,000 keys at a total cost of $20,000 in 2019, what is the variable cost per key?