Answer: 5
Step-by-step explanation:
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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:
$\boxed{ 2y-x=-4}$
First, subtract 7 on both sides. Now, you have 4x<1. Divide by 4 on both sides. Finally, you get x<1/4 (a quarter or said as one-fourth). So, x<1/4.