71+(-43)-13 give me the answer

In the diagram of circle a what is m

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?

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?