Why can't we use let instead of var?

Answer 1

we use let for constants and var for variables

Answer 2

Because we use let in constant.

Answer 3

You could use let in your own playground.
But in this case, the question is to put the TWO Variables together.
He doen't say the two Constants.
Why you can't here unlike your own playground?
because the boxes answer are predefined and the button Check , checks if there is var or something else.
Enjoy the App.

Answer 4

Where can't you use it? A value declared using a var can be changed later on, but a value declared using let cannot be changed