Question

Suppose people decide they no longer like plain shorts but they love plaid shorts. As a result, supply of plain shorts will decrease and shift to the right. supply of plain shorts will decrease and shift to the left. supply of plain shorts will increase and shift to the left. quantity supplied of plain shorts will decrease. quantity supplied of plain shorts will increase.

Answer 1

Well, since people no longer like plain shorts and move on to a substitute, there'll be a shift because of taste in preference. Since more people like plaid shorts, the supply of plaid shorts will increase, and for PLAID shorts, the supply curve would shift to the right.

However, since no one anymore wants to buy the plain shorts, producers will stop producing them as there'll be no more demand, therefore no more revenue.
Therefore, there'll be a decrease in supply (i.e. a shift to the left in the supply curve for plain shorts).