Steven K. answered 03/08/21
Harvard/Yale Grad with 25+ years teaching and tutoring
Because (x+9) is a factor of f(x), you can divide it into f(x)--use polynomial long division--to get the quotient =5x2+32x-21 without fractional remainder. Then factor this quotient to (5x-3)(x+7). Thus, the linear factors are (x+9), (5x-3), and (x+7). Check it by multiplying these three factors together!