The second one is the correct equation. The constant to the right should be the diameter squared, while the numbers inside the parentheses should be the opposite.
The equation is put in slope intercept form which is y=mx+b
The slope is m and in this case it is -1/2.
To find the y intercept substitute in 0
for x then solve.

Answer:
discrete and quantitative I think
That's an interesting fact but what is your question that's what I'm curious about?
Answer:
The answer is b = 6
Step-by-step explanation:
Area of a triangle= 1/2 × b × h
A = 21, h = 7, b = ?
21 = 1/2 × b × 7 (multiplying through)
21 = 7b/2
Cross multiply
2 × 21 = 7b
42 = 7b
b = 42/7
b = 6