When three edges meet, they form a point, which is called a vertex (the plural of vertex is vertices). A triangular prism has 5 faces, 9 edges, and 6 vertices.
30% of 42 is 12.6$. 42-12.6 = 29.4$ is the price of the pair with discount applied. Tax 7% 29.4 * 7% = 2.06 29.4$ + 2.06$ = 31.46 $ final price with discount and tax applied.
