V = 1/3 * area of base * height
NO is height.
sin(55) = NO/20
NO = 20 sin(55) = 16.38
find area of triangle using Heron's Formula:
s= (s1 + s2 + s3)2
area = [s* (s-s1)*(s-s2)*(s-s3)]**0.5
Here s1=13, s2=14, s3 = 15
plug values into formula to compute area
plug values of height and area of triangular base into formula for volume