Simplify the following text for a Grade 7 native English-speaking person.
Original: The National Gallery of Art is a national art museum , located on the National Mall in Washington , D.C. Open to the public free of charge , the museum was established in 1937 for the people of the United States of America by a joint resolution of the United States Congress , with funds for construction and a substantial art collection donated by Andrew W. Mellon .
Simplified: The National Gallery of Art is an art museum on the National Mall in Washington , D.C. . The museum was built in 1938 by the United States Congress .