Question 130380
The reason your answer is wrong is that your equation represents an infinite number of lines, one for every possible value of b which is the set of real numbers.  You have to find the particular y-intercept that is a point on the same line that passes through the point (1,-2).


When you are given the slope and a single point, use the point-slope form of the line:


{{{y-y[1]=m(x-x[1])}}} where {{{red(x[1])}}} and {{{red(y[1])}}} are the coordinates of the given point and {{{green(m)}}} is the given slope.


{{{y-red((-2))=green(3)(x-red(1))}}}


Now you can either leave it like that, put it into slope-intercept form by solving for y, or put it into standard form ({{{Ax+By=C}}}).


Slope-intercept form:
{{{y+2=3(x-1)}}}
{{{y+2=3x-3}}}
{{{y=3x-5}}}  (Do you see the difference between this answer and your answer?)


Standard Form:
{{{y+2=3(x-1)}}}
{{{y+2=3x-3}}}
{{{-3x+y=-5}}}
{{{3x-y=5}}}