Honestly, if you understand computer science and programming then get a score of 100 will be a cake walk for you . You can score 100 in economics too but compared to Computer science scoring 100 in economics might be tough.

The second factor that you must consider is what you want to do after class 12 th . Taking up science then computer science engineering is the best option for you as there are a lot of job opportunities in IT sector that will help you get a hefty package. If you want to go ahead in field of economics later then choose economics.