Given that

Substitute the value of x=1

f(1) = 0

That means  (x-1) is a factor for the given equation

Take 3 common

\ \ 3 is also a factor

Take (x+3) common

The remaining factors are (x+2) (x+3)

The  factors the given polynomial is (x-1) (x+2) (x+3)

Therefore the  roots of the given polynomial is (x-1) = 0 ==> x = 1

                                                                                   (x+2) =0 ==> x = -2

                                                                                  (x+3) = 0 ==> x = -3

The sum of the roots are 1 - 2 - 3 = -4