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?
So when adding fractions you need the same denominator so I chose to make 2/10 into the 100 denominator so you multiply 2/10 by 10/10 and you get 20/100 so you then add 45/100 + 20/100 and you get 65/100