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:
$\boxed{ 2y-x=-4}$
Answer:
773 and 869 and 703 on any day
Slope intercept form: y=Mx+b (where m is the slope and b is the y intercept)
So just put it into the equation
Answer: y= -8x + 4
100-16=84
84÷7=12
there are 12 students in the class because first you subtract 16 from 100 so you have that left then you divide that by 7 to find out how many students get 7 markers.