Steps:
1. Draw line segment BC of length 3.5 cm using ruler.
At B, construct an angle of measure 75∘. Draw a ray BX.
2. Cut a line segment BD equal to AB + AC = 6.5 cm on ray BX.
3. Join CD.
4. Draw the perpendicular bisector of CD, intersecting BD at point A.
5. Join AC.
6. ABC is the required triangle.