3.Erica is a citizen of a foreign country, and is employed by Fco, a foreign corporation that manufactures industrial equipment. Fco does not have a permanent establishment in the United States. Ericas job is to provide technical assistance to customers who purchase Fcos products. Many of Ericas customers are located in the United States. Consequently, Erica consistently spends about 120 working days per year in the United States. Erica does not possess a green card. Assume that the United States has entered into an income tax treaty with Ericas home country that is identical to the United States Model Income Tax Convention of November 15, 2006. How does the United States tax Ericas activities?