$92 \times 576 \div 2 \sqrt{1296} = (?)^{3} + \sqrt{49}$

Twenty-one times a positive number is less than its square by $100$. The value of the positive number is:

$\frac{3}{4} \left(1+\frac{1}{3}\right) \left(1+\frac{2}{3}\right) \left(1-\frac{2}{5}\right) \left(1+\frac{6}{7}\right) \left(1-\frac{12}{13}\right)$ is equal to

Evaluate $\frac{(2.39)^{2}-(1.61)^{2}}{2.39-1.61}$

What is the value of $\frac{(1.2)^{3}+(0.8)^{3}+(0.7)^{3}-3(1.2)(0.8)(0.7)}{(1.2)^{2}+(0.8)^{2}+(0.7)^{2}-(1.2)(0.8)-(0.8)(0.7)-(0.7)(1.2)}$?

$A$ man has some hens and cows. If the number of heads is $48$ and the number of legs is $140$,then the number of hens is: