For the first one, simplify the radicals. The 3 root 8 can be rewritten as 3 root 4 root 2, which turns into 6 root 2. The 4 root 3 can’t be simplified, so just multiply. 6*4=24 and the root 2*root 3 turns into root 6. So your answer for the first one is 24 root 6.
For the next one you can’t have a radical in the denominator so just multiply by root 3/ root 3, which gives you 6 root 3/3 which simplifies into 2 root 3.