Hints

1. Determine whether the lasagna is done

Use an if-statement to return a result based on some condition.
The task can be best solved when checking for the two specific conditions first.
Remember that missing parameters will be undefined and you can check whether a variable is undefined using the strict equality operator ===.

2. Estimate the preparation time

Use a default parameter to set the average preparation time in case it was not provided when the function was called.
Revisit arrays to find out how to determine the number of layers (length of the layers array).

3. Compute the amounts of noodles and sauce needed

First, set up two variables to track the amount of noodles and sauce. Define them with let so you can change the value later in your code. Also, assign an appropriate initial value.
Use a for loop to iterate through the layers.
If you encounter a 'noodles' or 'sauce' layer in your loop, increase the amount stored in the respective variable accordingly.
Use an object to return both results.

4. Add the secret ingredient

Revisit arrays to find out how to retrieve an element from an array and how to add something to the end of an array.
The index of the last element in an array a is a.length - 1.
The function should not have a return statement.

5. Scale the recipe

First, calculate the factor that you need to apply to all amounts based on the target portions.
One way to ensure the arguments is not modified is to use a new object to save the results.
Use a for...in loop to go through all the entries in the original recipe and fill the object accordingly.