Hi. I have 3 of 7 marks on this problem so far, looking for the other 4. I don't believe I have "shown clearly" that x^2+12x-160=0, but everything I've tried produces no more marks. I'm also not sure I've shown enough of the factorisation, but again everything I've tried has produced no more marks.

Mathswatch is notoriously selective when it comes to the phrasing of answers, so I'm hoping someone out there has answered this exact question with full marks and knows what Mathswatch expects to see here. Any help would be appreciated though.