Help Algebra 2

$f(x) = 4x^2 + 6x = 2x(2x+3)\\ \text{If this problem makes any sense at least one of these terms will be a factor of }g(x)\\ g(x) = 2x^2 + 13x + 15 = (2x+3)(x+5)\\ (f/g)(x) = \dfrac{f(x)}{g(x)} = \dfrac{2x(2x+3)}{(x+5)(2x+3)} = \dfrac{2x}{x+5}\\ \text{HOWEVER}\\ \text{There is a values of }x \text{ for which this is invalid}\\ \text{I leave it to you to identify these}$