To construct a line perpendicular to m, we need the help of a compass.
1. Place the compass on the given point P.
2. Draw an arc that crosses the m line on each side of the point P:
3. Place the compass over point A and measure the distance to point P. Now, construct and arc on the opposite side of the line m:
Then, distance AP will be the same to AC.
4. Do the same in the point B:
5. Use a ruler to join the given point P to the point where the arcs intersect C. Then, line PC will be perpendicular to line m:
With the help of your protractor you can measure the angle between PC and m and it has to be 90 degrees.