Final answer:
The correct value of p when completing the square of the equation b² - 12b + 20 = 0 is 16, calculated by squaring half of the coefficient of b (which is 6) and subtracting the constant 20.
Step-by-step explanation:
The quadratic equation provided is b² - 12b + 20 = 0. When Mariah completes the square, she rewrites it in the form (b - h)² = p, where h is half of the coefficient of b (which is 6 in this case), and p is the constant term that will make the left side of the equation a perfect square.
We can find p by taking the square of half of -12, which is 6, and then subtracting the constant term of the original equation, 20. Calculating this gives us (6)² - 20 = 36 - 20 = 16. Therefore, the correct value of p is 16, which corresponds to option C.