What is the rate of change (8,13), (-13,-15)

Rewrite the following without an exponent. (5/8)-1

Tod does not have any cookies. david gives jeff 8 cookies. then he splits half of the cookies he has left with tod. david let’s c represent the number of cookies that he starts with. he finds the number of cookies that tod has is 1/2 the difference of c and 8. write an expression to represent the number of cookies that tod has.

Which equation represents the function on the graph?