An SQL query cannot only find data which already exists in a table, but also values which may be calculated from this data.
First the daily prices of the single rooms of all hotels are to be selected:
SELECT hno, roomtype, price
FROM room
WHERE roomtype = 'single'
To obtain the weekly price of a hotel room, the statement can be formulated in the following way:
SELECT hno, roomtype, price*7 price_of_week
FROM room
WHERE roomtype = 'single'
'price*7' is an expression. The weekly price is calculated as the result of the multiplication of 'price' by 7.