No problem with your grades... the only thing is the interview,
essay writing... SAT with about 1200 should be enough to get in.
However, I think the criteria may be more stringent for the
Economics course as the intake is only 50 students. The alternative
would be to apply for Economics as the first choice, and Business
mgmt as the second choice. When you are accepted into the uni, you
can always try to opt for a double degree (this is of course
subjected to grades as well, as only a portion of students would be
accepted for double degree. 
Essay and interview are equally important, cos interpersonal skills
are very crucial, and note that participation is an important
criteria in our school coursework; thus, it is always preferred
that you are one that can speak up in class..otherwise, there may
be some difficulties too. Just go ahead and apply... good luck
