If f(x) and f-1 (x)
are inverse functions of each other and f(x) = 2x+5, what is f-1 (8)?

For this case we have the following function:

 f (x) = 2x + 5

 Clearing x we have:

 2x = y - 5

 x = (y-5) / 2

 Rewriting:

 f (x) ^ - 1 = (x-5) / 2

 Evaluating x = 8:

 f (8) ^ - 1 = (8-5) / 2

 f (8) ^ - 1 = 3/2

 f (8) ^ - 1 = 3/2

 option 2

i believe it is c.y = 9x

rise over run. 9 units up over 1 unit right or 9/1