Can someone help me with number 30? :)

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

Write a function rule for  “the output is  5 less than the input.” let  x be the input and let  y  be the output.

Function 2 f(x) = -x2 + 2x - 15 function _has the larger maximum. (put 1 or 2 in the blank space) numerical answers expected! answer for blank 1: