4 years
A bid of $16m does not qualify for a four year contract. The minimum 4 year contract is $22.0m = $5.5m (2021). The best you can do with a $16.0m winning bid is $5.5m (2020). Would you like to increase your winning bid amount to $22.0m so you can have the extra year at $5.5m?
$5.5m (2020) or $5.5m (2021) -- which do you prefer?