Let x represent input and y represent output.
We are asked to write function rule for each of the given verbal description.
(a) The output is five less than the input.
This means that y is 5 less than x. So we will subtract 5 from x and equate with y as:

Therefore, our required expression would be 
.
(b) The output is one fourth the input.
This means that y is 
 of x. So we will multiply x by 
 and equate with y as:

Therefore, our required expression would be 
.
(c) The output is one more than twice the input.
The twice of the input would be 2 times x that is 
.
One more than twice the input would be 
 plus 1 that is 
.
Now we will equate 
 with y as:

Therefore, our required expression would be 
.