Answer:
Limiting the price of a gallon of gas to $2 - Price Ceiling
A price ceiling occurs when the goverment imposes a maximum price on a good or service. In this case, limiting the price of a gallon of gas to $2, meaning that the price of it is not allowed to go higher than that, is an effective price ceiling.
Charging a 50 percent tariff on imported cotton - Trade restriction
A tariff is the most common trade restriction. A tariff is simply a tax on imported goods, and has the main goal of protecting domestic producers from foreign competition.
Requiring that all workers be paid at least $5.15 per hour - Labor law
Labor law, as the name implies, regulates all matters related to labor. A minimum wage is a labor law, and it is also a price a floor: a government mandated minimum limit on the price of labor.