To draw the triangle do the following steps:
i) Draw BC as 8 cm.
ii) Now from point B draw an angle of 45⁰.
iii) Then mark 3.1 cm on 45⁰ line. Mark it as D. Join CD
iv) Draw the perpendicular bisector of CD and let it intersect the 45⁰ line. Mark that point as A. Join AC. ABC is the required triangle.
Hope that helps !!