Question 1172916
Getting started  {{{P=-25(x^2-38x-120)}}}


and completing the square inside the grouping, {{{P=-25(x^2-38x+(38/2)^2-120-(38/2)^2)}}}


{{{P=-25(x^2-38x+19^2-120-19^2)}}}


You can continue and finish from here.