What is the value of arccos(−1/2)in radians?

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

Evaluate the expression for the given value of the variable. 5×(h+3) for h=7

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?