the answer would be 9(8b+5)
this is how you do it...
1. find the GCF of both numbers in this one the GCF would be 9
now, what do you multiply 9 by to get 72... 8, so 8 would go into the parenthesis and because there is a variable there which is 'b' the 8 would become '8b' now what do you multiply 9 with to get 45? '5' so you would add 5 into the parenthesis and that would be your answer!
Hope this helped! :D