Question

Solve m =y-y1/x-x1 for y

Answer 1

I assume you are working with the point-slope form of a line. A little spacing would make things more readable:

m = (y - y1)/(x - x1)

Clear the fraction:

m(x - x1) = y - y1

Now add y1 to both sides, and we have

y = m(x - x1) + y1

or, in slope-intercept form,

y = mx + (y1 - m*x1)

Note how the slope m appears as the coefficient of x, as expected.