JavaScript Coding Challenge Objects

I’m new to coding so please forgive me it this is simple and any bad code. The question is:

Here’s an example problematic kitchen

const kitchen = {
  hasFridge: true,
  favouriteAppliance: 'KeTtlE',
  food: 'eGgS',
  shelvesInCupboards: 3,
  shelvesNotInCupboards: 2,
  petName: 'RhuBarB',
  hoover: 'DysOn'
};

To sort out our kitchen:

1. Fix the jumbled string values – replace them all with versions that are all lowercase
2. Remove the hoover property – hoovers don’t belong in the kitchen
3. We only need to know the total number of shelves. If shelvesInCupboards and/or shelvesNotInCupboards are present, delete these keys
4. Add a key of totalShelves which is equal to the sum of the values that were under shelvesInCupboards and shelvesNotInCupboards.

A fixed-up version of the above example kitchen should look like this, though remember that object properties are not ordered, so it doesn’t matter if your properties appear to be in a different order.

const kitchen = {
  hasFridge: true,
  favouriteAppliance: 'kettle',
  food: "eggs",
  petName: 'rhubarb',
  totalShelves: 5
};

The preset code is:

function sortTheKitchen(kitchen) {

    // Don't change the code below this line
    return kitchen;
}

I’ve gotten up to here so far but I am confused about the how to tackle parts 3 and 4 of sorting out the kitchen.

function sortTheKitchen(kitchen) {

    for (let key in kitchen) {
        if (typeof kitchen[key] === 'string') {
            kitchen[key] = kitchen[key].toLowerCase();
        }
    }

    delete kitchen.hoover;
    kitchen.totalShelves = (kitchen.shelvesInCupboards + kitchen.shelvesNotInCupboards);
    delete kitchen.shelvesInCupboards;
    delete kitchen.shelvesNotInCupboards;

    return kitchen
}

Thanks for any help you can provide.