I think that if op wants to major in economics, then he should transfer internally from Arts to Commerce. I also agree with Alter though. A 75 average is quite hard to maintain, especially when you're a first year student and completing your first semester, and you are completing subjects which you dislike. However, it is doable. I know many science students who completed an Arts core as their breadth and scored a H1/H2A overall despite there being a general limit on the amount of H1s that are given out (applies to some Arts subjects if I'm not mistaken?) So if you want to major in Economics I suggest you do it in Arts and then transfer, otherwise, do it at another uni to get some subjects credited and save time.