The polynomial h2-9hs+9s2 cannot be factored out to anything simpler. However, if there is a typo and the polynomial is supposed to read h2-6hs+9s2 then you can factor it be remembering F.O.I.L. (First, Outside, Inside, Last) and performing it in reverse.
So, to get the h2, the two factors must begin with "h". Then to get the last part "+9s2, both factors must end with + or - 3s. And because the middle part is a negative 9hs, it means that the 3s must have a negative sign. So the two factors are (h-3s) (h-3s), or (h-3s)2 in complete factorization.
Performing F.O.I.L. on this gives h2-3hs-3hs+9s2, or h2-6hs+9s2.