Find index with highest sum. Not sum of array. Sample: [11-11-11,22-22-22,33-33-33]

I need to find the index in an array with the highest sum. The array looks like this: [11-11-11,22-22-22]. So index [0] would equal 6. Also, if the highest sum matches another the last should be returned. I'm seeing a Max.array.length , a for/if/else statement maybe. If anyone can give me a hint I would appreciate it.