(x+2)(x+4) = x²+6x+8 show the steps

The lengths of two sides of a triangle are 9 and 15. what can be said about the length of the third side? a. it must be greater than or equal to 6 and less than 24. b. it must be greater than or equal to 6 and at most 24. c. it must be greater than 6 and less than 24. d. it must be greater than 6 and at most 24.