$A$ student was asked to find the arithmetic mean of the numbers $3, 11, 7, 9, 15, 13, 8, 19, 17, 21, 14$ and $x$. He found the mean to be $12$. What should be the number in place of $x$?

The average salary of $20$ workers in an office is $Rs. 1900$ per month. If the manager's salary is added,the average becomes $Rs. 2000$ per month. The manager's annual salary (in $Rs.$) is

The average marks obtained by $180$ students in an examination is $50$. If the average marks of passed students is $80$ and the average marks of failed students is $40$,then what is the number of students who failed the examination?

The average price of $80$ computers in an electronic shop is $Rs. 30,000$. If the highest and lowest price computers are sold out,then the average price of the remaining $78$ computers is $Rs. 29,500$. The cost of the highest price computer is $Rs. 80,000$. The cost of the lowest price computer is (in $Rs.$): (in $,000$)

Out of $9$ persons,$8$ persons spent $Rs. 30$ each for their meals. The ninth one spent $Rs. 20$ more than the average expenditure of all the nine. The total money spent by all of them was (in $Rs.$)

In a family,the average age of father and mother is $38 \text{ years}$,whereas the average age of father,mother,and their only daughter is $28 \text{ years}$. Then,the age of the daughter is? (in $\text{years}$)