Step 1:
Draw the base line AB of the length 7 cm.
Step 2:
Measure the angle A with your protractor. Make a mark at 75⁰ and draw a line from A passing through the mark.
Step 3:
Cut an arc of radius 4 cm on the line passing through the point A. The point where this arc cuts the line is the point C.
Step 4:
Draw a line from B to point C to get the required ∆ABC, as shown below.
From the above construction, we see that length of side BC is 7.1 cm.