18) What is the name of triangle with three sides are equal and three angles are equal?

19) What is the name of triangle with all the three sides are unequal in length and all the three included angle are also unequal?

20) What is the name for classification of letters having the elementry strokes of even width?

21) What is the name for part of circle with radii making 90? with each other?

22) What is the name for part of circle, between any two points on the circumference or periphery?