How many square feet will somebody need to cover the entire floor if it was 15 ft. by 18 ft

Which shows the pre image of triangle xyz

How do i do this activity, is appreciated

David is spreading mulch on a triangular area of his flower bed. the coordinates of the vertices of the area are (1, 3), (9, 3), and (4, 6). what is the area of the triangle if each square has an area of 3 square feet?