Answer:
10
-1
Process finished with exit code 0
Explanation: see code bellow
public class BinarySearchRecursive {
    public static int binarySearch(int[] a, int key) {
        return binarySearchRecursiveHelper(a, key, 0, a.length - 1);
    }
    public static int binarySearchRecursiveHelper(int[] arr, int target, int start, int end) {
        if (start > end) {
            return -1;
        }
        int mid = (start + end) / 2;
        if (arr[mid] == target) {
            return mid;
        } else if (target < arr[mid]) {
            return binarySearchRecursiveHelper(arr, target, start, mid - 1);
        } else {
            return binarySearchRecursiveHelper(arr, target, mid + 1, end);
        }
    }
    public static void main(String[] args) {
        int[] a = {-4, 2, 7, 10, 15, 20, 22, 25, 30, 36, 42, 50, 56, 68, 85, 92, 103};
        int index = binarySearch(a, 42);   // 10
        System.out.println(index);
        index = binarySearch(a, 66);   // -1
        System.out.println(index);
    }
}