How would you add a new column namely 'val' to a dataframe df that has 10 rows in it and has columns as 'Item', 'Qty', 'Price' ? You can choose to put any values of your choice.

Write code statements for a dataframe df for the following :

(a) delete an existing column from it.

(b) delete rows from 3 to 6 from it.

(c) Check if the dataframe has any missing values.

(d) fill all missing values with 999 in it.

Write statement(s) to delete a column from a DataFrame.

Write statement(s) to change the value at 5th row, 6th column in a DataFrame df.