AB ⊥ l, B ∈ l, M ∈ AB , AM = 7 in, AB = 15 in.
Here AB is a line segment which is perpendicular to line I.
Point B lies on line I,and Point B lies on line segment AB.
⇒AB=15 [Given]
⇒AM+MB=15
⇒AM=7[given]
⇒7+MB=15
⇒MB=15-7
⇒MB=8in
So,the length of line segment MB is 8 in.
The same thing is depicted in the diagram.