1) Draw line GO as base of parallelogram.
Sum of adjacent angles of parallelogram =180
So angle O=60=> angle G=180-60=120(As O and G are adjacent angles)
Draw angle 60 at O and angle 120 at G
Now extend parallel lines OT from O and GU from G such that if you join points T and U ,TU=10Cm
As oppsite sides of parallelograms are equal