Answer & Explanation:
1. A steel tariff increases the price of steel : Increase in of 'Price of inputs' - decreases (leftward shifts) supply curve
2. Improvement in robotics increase efficiency & reduces costs : Upgradation of 'technology'- increases (rightward shifts) supply curve
3. Factories close because of am economic downturn : 'Number of sellers' reduce - decreases (leftward shifts) supply curve.
4. The price of trucks falls, so factories produce more cars : Decrease in 'price of related goods' - increases (rightward shifts) supply curve.
5. The government announces a plan to offer tax rebates for the purchase of commuter rail tickets : 'Expectations' regarding rise in relative price of cars - decreases (leftward shifts) supply curve.
6. The government announces that it will dramatically rewrite efficiency standards, making it much harder for automakers to produce their cars : 'Goverment policy' stringency - decreases (leftwards shifts) supply curve.