Which function has an inverse that is a function ?

Answer:
[tex]m(x)= -7x[/tex]
Step-by-step explanation:
A fuction has an inverse if it passes vertical line test.
[tex]b(x)= x^2+3[/tex] is a horizontal U shaped graph . when we draw a vertical line then it crosses the inverse graph at two points. So it is not a function.
[tex]d(x)= -9[/tex]
Inverse graph is a vertical line that does not pass vertical line test. so it is not a function.
[tex]m(x)= -7x[/tex]
Inverse graph is a graph of a line (linear function). Linear function always passes vertical line test. Inverse is a function
[tex]p(x)= |x|[/tex]
Inverse of absolute funciton does not pass vertical line test, so it is not a function.