Final answer:
An increase in t-shirt supply leads to a surplus at the original price and a decrease in the t-shirt price due to a rightward shift in the supply curve caused by lower production costs.
Step-by-step explanation:
An increase in the supply of t-shirts brings a surplus of t-shirts at the original price and a decrease in their price. When technology improves and production costs reduce, companies are able to supply more at any given price, shown by a rightward shift in the supply curve. For instance, if the cost of manufacturing t-shirts drops, producers are willing to supply more t-shirts at the same price, creating a surplus. As a result, to sell this increased supply, the price of t-shirts will typically decrease.