The formula of linear equation is:

Where
x1 and x2: x coordinates(-1 and 3)
y1 and y2: y coordinates(-2 and 10)
m is the slope
We can then choose a point from the line to find the eqaution.
We need to first find the slope:

In this case:

In this case, as the y2 is given as 1,put (-1,-2) , and the slope(3 )into the eqaution :
y-(-2) = 3(x-(-1))
y+2 = 3(x+1)
Therefore

is the answer.
Hope it helps!
7 because the 3 is the coefficient and the x is the variable. The + is the operator so that leaves you the 7
The answer is B.Center (2 -8) Radius =4