How to solve an algebra equation. How to find the equation of a line.?

1a. You can find the equation of a line with two given points on the line with slope-intercept form (y=mx+b). You just need to find the slope(m) and the y-intercept(b).  First, you find the slope (m) using the two given coordinate points. Find the difference between the y variable of the first coordinate, from the y variable of the second coordinate.  Divide this number by the difference between the x variable of the first coordinate and the x variable of the second coordinate.  For example;

(3,6)  (7,4)       x(1)=3, y(1)=6
                      x(2)=7, y(2)=4

6-4=2
3-7=-4

m=-(1/2)

Now that you have slope, you can use one of the given coordinates and plug the x and y in the slope-intercept form equation, to find the y-intercept(b). For example using the coordinate (3,6);

y=-(1/2)x+b
6=-(1/2)(3)+b
b=15/2 (or 7.5)

Now you have the equation of the line in slope-intercept form:
y=-(1/2)x+15/2

As for 1b. I really don't understand your question, but if you want to clarify I'd be glad to help!

Hope this helps! Let me know if it's clear or not