You are given a data frame store that contains information on items, their prices, and the quantities sold in a small furniture shop:

Item	Price	Sold
Sofa	340	67
Armchair	150	81
Dining table	115	79
Bookshelf	160	42
Kitchen cabinet	70	67

Your tasks are:

1. Add a new column named 'Revenue' with the revenue of each item (multiply 'Price' and 'Sold'). To access columns, use the $ sign.
2. Using the sum() function, calculate the total number of items sold. Save in items_sold variable and output its value.
3. Calculate total revenue using sum() function. Save in the total_revenue variable and output its value.
4. Find out the average price of the sold item - divide total_revenue by items_sold.