1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

x = int(input())
for i in range(x):
    m = int(input())
    l = list(map(int,input().split()))
    o = max(l)
    if sum(l) // m == o:
        print(-1)
    else:
        for i in range(len(l)):
            if l[i] == o:
                if i < len(l)-1:
                    if l[i+1] != o:
                        print(i+1)
                        break
                if i > 0:
                    if l[i-1] != o:
                        print(i+1)
                        break