It probably is c because every one knows c is always right
No given information.
No answer possible.
First:
Divide everything by 9/5, or multiply by 5/9, in order to remove the multiply 5/9 from c.
This results in:
F(5/9) = c + 160/9
Then just move the 160/9 to the other side to get:
c = 5/9F - 160/9
This senecio is in reliable because how do you know if the people at the sand which shop next door are frequant customers