Which of the following sets of data does not represent a function?

set a
x
y
6
3
8
4
5
7
9
2

set b
x
y
0
3
1
8
2
8
3
-7

set c
x
y
10
7
20
11
30
9
40
7

set d
x
y
3
9
2
2
8
-3
2
1
a.
set a
b.
set b
c.
set c
d.
set d

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?