ooh this is tricky
you cant factor it further because 17 is a prime number,
we know that the factored out form is either
(3+/-number)(21+/-number)
(2+/-number)(14+/-number)
(6+/-number)(7+/-number)
and we know that the signs must be different because opppositie signs multipied togethter=negative and 15 is negative
I don't have a foolproof way to find the answer. you must use trial and error
the answer is (6x-5)(7x+3)