Final answer:
In a competitive labor market for house painters, an increase in the demand for house painting services would increase the demand for house painters, leading to a rightward shift in the demand curve.
Step-by-step explanation:
In a competitive labor market for house painters, the factor that would increase the demand for house painters is c) An increase in the demand for house painting services. This is based on basic principles of supply and demand where an increase in demand for a service would lead to an increase in the number of workers needed to provide that service. This can be considered a rightward shift in the demand curve. Conversely, if there is an increase in the price of paint or a decrease in the cost of paintbrushes, it primarily affects the supply side by influencing the cost of production, rather than directly affecting the demand for house painters. A decrease in the number of houses being built would likely decrease the demand for house painters, as there would be fewer houses requiring painting services.