THis is a cool question.
1) Use the point slope form to find the equation of the lines between two of the points (choose two points that when a line is drawn between them make a chord on the circle).
2) Use the midpoint of a line equation to find the midpoint of the line, then find the slope of the line that is perpendicular at that point and write an equation for it.
3) Then do the same thing for the other two points that form a chord on the circle.
4) Then set the two equations equal to each other and solve. The point where they meet is the circumcenter.
Answer:

Step-by-step explanation:

Answer: 6.25
Step-by-step explanation:
Because corresponding sides of similar triangles are proportional,

Answer:
16
Step-by-step explanation:
Let's give letters as the image. Triangle ABH is a right triangle, so you can apply pythagoream theorem. In particular, it's the classic "3-4-5" triangle (there are some triplets of integers that gives you a right triangle, and 3-4-5 is the most famous). Either way, the height of the triangle is 4.
At that point you can compute the area by multiplying base and height, and the total surface is 16.
(1,3) , (2,7), and (3,11):
Let's find the slope m between (1,3) and (2,7)
Slope = Rise / Run
m = (7-3) / (1)
m = 4.
Our equation y=mx +b has a slope of 4. Since C is the only option that satisfies this, we already know the answer, but let's find the y-intercept.
y = mx + b. Plug in 4 for m, and the first coordinate (1,3) for x and y
3 =4(1) + b Subtract 4 from both sides
b = -1
Our function is y =4x - 1
Answer is C) y=4x-1