These two are fundamentally different subjects. If you can, open a brochure/prospectus right away and look at the course description and details for both courses. You could also check this online.

Civil is related to construction of buildings, bridges, roads etc, while biomedical engineering does not pertain to biology or chemistry. Rather, it involves medical physics (diagnostic equipment etc).

I have seen some course info for Biomed Engineering and although it is engineering all the same, it does not have quite as high entry requirements (for 1 particular example) as that of electrical or mechanical engineering. Also, environmental would have a lower req. than electrical or mechanical.

It's obvious that Further Mathematics would be much more advantageous to such a student than Economics, given that Further Mathematics builds on Mathematics and also has topics not found in Mathematics, and that some undergraduate engineering degrees only require A level Mathematics (as an entry prerequisite). Engineering would use calculus, pure mathematics, linear algebra, analysis, probability, statistics etc on a far greater scale than Economics. This is a question that begs to be shot down in disgust.

If you were to take those 4 subjects at A level, your degree choices would be nearly limitless. You could apply for the titular courses of course, being Mathematics, Physics, Chemistry, and Economics, and also Medicine, Dentistry, Veterinary Science/Medicine, Pharmacy, Health Sciences, Occupational Health, Natural Sciences, Physical Sciences, Geology, Petrology, Engineering (almost all kinds, even some variants of Bioengineering), Statistics, Computer Science/Discrete Mathematics/Programming, Information Technology, Computer Engineering, Software Engineering, Finance, Business, Financial Mathematics, Econometrics, Accounting, Investment, Management/Operational Research/Decision Sciences, Politics, Philosophy, Law, Anthropology, Sociology etc.

I don't know the job market well, but you don't need an undergraduate degree to easily get RM2500 per month without being a salesperson/sales executive/sales agent or telemarketer, with little or none work experience.