We have two base angles that are congruent, so that implies we have an isosceles triangle. With isosceles triangles there are exactly two congruent sides. So PD = PC = 20
Each leg of each triangle is equal to 42 ft. The reason why is because we have congruent triangles so all of the corresponding parts are congruent. For any given right triangle, the two legs are equal in length.
We have 4 sections of 42 ft, so 4*42 = 168 ft in total
Note these three properties: Property 1: a+b = 5+4 = 9 is larger than c = 2 Property 2: b+c = 4+2 = 6 is larger than a = 5 Property 3: a+c = 5+2 = 7 is larger than b = 4
Since all three properties hold true, this means that we can construct a triangle with these side lengths. Put another way, take any two sides and add them up. The result being larger than the third side allows a triangle to be formed. This is the triangle inequality theorem.
Here is the graph for y = (x + 0.25)(x - 1.75) which will look like yours. There are all sorts of variations that are possible, but at least I could reproduce a similar looking graph.
