Congruent shapes are shapes that share the same side lengths and angle measures. In figure 1, we see that all sides and angles are marked equal, thus both shapes are congruent. However, in figure 2, we clearly see that the sides of each of the triangles are different. Thus, the triangles in figure 2 are not congruent.
18 3/4 is equal to 18.75, so 18.75x2.80 is your original cost (52.5). After doing that, since 52.5=100% you are going to divide 52.5 by 5 since 20x5=100. So 20% is 10.5. 52.5-10.5= $42.00