The sum of squares of two numbers is $68$ and the square of their difference is $36$. The product of the two numbers is

$21.9 \%$ of $(511.987 - 42.49) = \frac{?}{5.5}$

$\sqrt{6+\sqrt{6+\sqrt{6+\cdots}}} = ?$

In a two-digit number,the digit in the unit's place is $1$ more than twice the digit in the ten's place. If the digits in the unit's place and the ten's place are interchanged,the difference between the new number and the original number is $1$ less than the original number. What is the original number?

$[(7.98)^{2} - (13.002)^{2} + (4.02)^{3}]^{2} = ?$

The product of two numbers is $120$. The sum of their squares is $289$. The sum of the two numbers is