Why error comes when '17' * '7'

Question

in detail answer

Answer 1

you can't multiply a string by a string :)
the * operator works only for a combination of:
- a string and an integer
- an integer an an integer
- a float and a float
- ...
but not with a string and another string

Answer 2

So basically it should be '17 * 7'
you dont need to single string