Question

critical point of 5(x + 3)(x-7)

Answer 1

what's the derivative you got?

Answer 2

differentiate it first,
solve for x equate it to zero

Answer 3

also remember, you specified critical point not critical number... so you must give x, y coordinates

Answer 4

got it

Answer 5

if you got tired sometimes of usual stuff, you can always do
http://www.wolframalpha.com/input/?i=extremum+5%28x+%2B+3%29%28x-7%29