You need to be more specific when referring to an element in an array. Since myArray is a list of numbers, we need an indexto access one of the numbers.
myArray is the whole list. myArray , myArray , are each one number in that list.
The for loop uses the variable i to visit each element, one at a time. Therefore, your code needs the index. Try myArray [i] = myArray [i] + 5;