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

for _ in range(int(input())):
	n = int(input())
	a = list(map(int, input().split()))
	m = max(a)
	for i in range(1, n):
		if a[i]>a[i-1] and a[i]==m:
			print(i+1)
			break
		elif a[i]<a[i-1] and a[i-1]==m:
			print(i)
			break
	else:
		print(-1)