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

# cook your dish here
import math
for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    x=min(a)
    y=max(a)
    if(x==y):
        print(-1)
    else:
        for i in range(n-1):
            if(a[i]!=y and a[i+1]==y):
                print(i+1+1)
                break
            elif(a[i]==y and a[i+1]!=y):
                print(i+1)
                break
            
    