The circumference of a circle is 25.12 centimeters. calculate the radius of the circle

It's abvious he round

as 3.14 so we write the formula and equal it to 25.12 which is:
25.12=2πr
then put 3.14 instead of

there you go! we got a equation
then r is 4

I can't answer all of the questions but I can help.
I'll use problem 3 as an example. I'll use point H and point G for this. Point H is located at (6, 5); point G is located at (1, 7).
Choose your y1 and y2 (any y from point H or point G, it doesn't matter) and your x1 and x2 (still doesn't matter if you choose the x from point H or G).
Next, you set up the equation like this:

You solve the equation by subtracting your y1 and y2 and that will be your numerator, then your chosen x1 and x2, which will be your denominator.
Your answer will be the slope. Hope that helps! Sorry if it was a confusing explanation, if you need more help then feel free to ask. :)