[
    {
        "size": [
            6,
            6
        ],
        "difficulty": 3
    },
    {
        "size": [
            10,
            10
        ],
        "difficulty": 3
    },
    {
        "size": [
            15,
            15
        ],
        "difficulty": 3
    },
    {
        "size": [
            20,
            20
        ],
        "difficulty": 3
    }
]