E2 reaction - strong base
It will be more difficult for sterically hindered bases to remove the proton of the β-carbon having the fewest hydrogen substituents, since this carbon atom has more bulky groups around it compared to the the others. So base 3, being the less hindered base, will provide a higher percentage of the major Zaitsev’s product and base 2 will provide a higher percentage of the minor product compared to the other bases.