Let's break down the question: ### **Question** A line AB of length 85 mm is inclined 45 degrees to the horizontal plane and 60 degrees with the vertical plane. Calculate the length of the projection in front view on vertical plane. ### **Solution** The length of the projection of the line on the vertical plane (front view) is given by: \[ \text{ of projection on vertical plane} = \text{True length} \times \cos(\text{angle with vertical plane}) \] Given: - True length (\(L\)) = 85 mm - Angle with vertical plane (\(\theta\)) = 60° \[ \text{Projection} = 85 \times \cos(60^\circ) \] \[ \cos(60^\circ) = .5 \] \[ \text{Projection} = 85 \times .5 = 42.5\, \text{mm} \] ### **Correct Option** - **42.5 mm** --- **Answer:** The correct option is **42.5 mm**.