3root(3)(2)+5root(3)(16) needs to be simplified in order to add.In order to add radicals, index and radicand(inside the radical) need to be the same.
Here is how you add the expression: 3root(3)(2)+5root(3)(16)= 3root(3)(2)+5root(3)(8*2)= 3root(3)(2)+5(root(3)(8)*root(3)(2))= 3root(3)(2)+5*2*root(3)(2)= 3root(3)(2)+10root(3)(2)= 13root(3)(2)