Hello.
Okay, so you found the gradient of the line, which is -1/2.
A perpendicular line is one that has a negative reciprocal of the original line (above line). That is, if m is the gradient, then the gradient of the perpendicular line is -1/m. So, this means that the gradient of the perpendicular line is -1/-1/2 which is equal to 2.
So, the perpendicular line has gradient 2 (m=2) , so it has equation y=2x+c. Then, you sub in the point (-2,1) where you substitute x=-2 and y=1 to get the value of c.
So: 1=2(-2)+c which is 1=-4+c. Add 4 to both sides. 1+4=c. Thus, c=5.
Then you have your equation y=2x+5
With these questions where you need to find the parallel line or the perpendicular line, you need to ONLY consider the
gradient. The gradient is important. In a parallel line, the gradient is the same while for a perpendicular line, the gradient is a negative reciprocal where if m is the gradient of the original line, the gradient of the perpendicular line would be =-1/m.