Hello,

If there is a timing discrepancy, you can write both exams together. Actually you  really need not to study extensively for Bcom exams, because most of the bcom syllabus will be automatically covered in your foundation course. If both exams fall on the same timing then you have to skip one. In that case you have to decide yourself  which exam is really important to appear. If foundation exam is more important to you then go for it. And you can be in the CA course, if you clear the foundation exam. Later you can give bcom supply paper.