(n-21)/2=4n is the equation
First, divide what is in the parentheses by 2
0.5n-10.5=4n
Then, multiply the whole equation by 2 so we have all whole numbers
n-21=8n
Move N so that it is with 8n
7n=-21
Divide 21 by 7
n=-3
Solution: The number (n) is equal to -3
The given equation is: 
To find the line perpendicular to it, we interchange coefficients and switch the signs of one coefficient.
The equation to a line perpendicular to it is:
$ 2y-x=c$
where, $c$ is some constant we have determine using the condition given.
It passes through $(2,-1)$
Put the point in our equation:
$2(-1)-(2)=c$
$c=-2-2$
$c=-4$
The final equation is:
$\boxed{ 2y-x=-4}$
Step-by-step explanation:
You multiply the two other sides by itself like 12x12=144 and do that for all the sides that you know then you add up all of the numbers you got from adding like 144 plus 64 equals 208 and then 208 is the hypotenuse.