In this diagram, the area of the large square is equal to the combined areas of the tilted square and the four right triangles. (the picture)
When written as an equation, this relationship can be simplified algebraically, as shown in these 4 steps.

Step 1: (a + b) (a + b) = c2+ 2ab

Step 2: a2 + 2ab + b2 = c2 + 2ab

Step 3: a2 + 2ab ─ 2ab + b2 = c2 + 2ab ─ 2ab

Step 4:

What equation fits in the box in Step 4 to complete the proof

(part B)
Builders use the equation from Part A to determine the number, height, and depth of stairs necessary to extend from the first floor to the second floor of a building.

Given that the ceiling is 12 feet high, stairs are 8 inches high and the stairwell is 16 feet long, describe in detail how a builder could use the equation to determine the number, height, and depth of the stairs.