The given side dishes are rice potatoes and vegetables = 2
The given main dishes are chicken, fish and beef = 3
As there are 2 side dishes. With rice potatoes we can order any of the three main dish, so it is 3 combination. Similarly with vegetables also, we can order any of the three main dish, so it is 3 combination.
So, combined combination is 3+3 = 6
Hence, the correct answer is option A.