想两个NFT的属性值，相加之后的值赋给需要升级的NFT，再销毁另外一个nft。

struct Prop{
        uint16 power;        //属性值
    }

    mapping(uint=>Prop) public props;

//升级
    function upgrade(uint256 upId,uint256 burnId)public{
        require(ownerOf(upId)==msg.sender,"player and upId not matched");
        require(ownerOf(burnId)==msg.sender,"player and burnId not matched");
    props[upId];
    props[burnId];
        Prop memory i;
        i.power=需要升级的NFT属性值+需要销毁的NFT属性值;
        props[upId]=i;

        burn(burnId);
    }

提示struct 数组不能运算，请问哪位大神知道怎么解决吗？先谢谢了！！