(1) since from the initial state in the given NFA, if one encounters even number of a's , then and only then reaches final states. For example, from state S , for string "aaaa", one reaches the bottom right-most state. But, as one can notice, it also has an epsilon-transition to S, which is a final state. Hence, we can conclude here that this NFA accepts strings having even number of a's.
Design of DFA is pretty trivial and hence, left as an exercise for the person who asked this question.
Thank You.