If doubling a number and adding $20$ to the result gives the same answer as multiplying the number by $8$ and taking away $4$ from the product,the number is

Which number should replace both the $*$s in $\left(\frac{*}{21}\right) \times \left(\frac{*}{189}\right) = 1$?

$(21.5 \% \text{ of } 999)^{1/3} + (42 \% \text{ of } 601)^{1/2} + ? = 28$ (Assuming the equation equals $28$ for a standard evaluation)

If $\frac{1}{2}$ is added to a number and the sum is multiplied by $3,$ the result is $21.$ Then the number is (in $.5$)

When $335$ is added to $5A7$, the result is $8B2$. $8B2$ is divisible by $3$. What is the largest possible value of $A$?

The numerator of a fraction is the product of two numbers. One of the numbers is greater than the other by $2$. The greater number is smaller than the denominator $D = 7+c$ (where $c > -7$ is a constant). If the fraction is $f(x) = \frac{(x-2)x}{x+k}$ (where $x$ is the greater number),find the minimum value of the fraction.