It should have 2 solutions
7x - 1 = 5x - 8
Minus 5x on each side
2x -1 = -8
Plus 1 on each side
2x = -7
Divide by 2 on each side
x = -7/2
The number is most likely -7/2
take your compass on a point on your line. then draw a circle. take the 2 points in which the circle hit the line and draw 2 circles larger than half the distance between he 2 points. take the point that they intersect and and connect it to the line and you point M and it is purpendicular. does that make sense?