1. Draw the base BC 7.5 cm and at point B make an angle say XBC of 45 degree.
2. Cut line segment BD equal to AC - BC (2.5 cm) from line BX extended on opiate side of BC.
3. Join DC and draw perpendicular bisector, say PQ of DC.
4. Let PQ intersect BX at A. Join AC.
Thus, ABC is the required triangle.