When you're given a point and the slope of a line, it is often easiest to write its equation in point-slope form.
This is [tex]y-y_1=m(x-x_1)[/tex], where [tex](x_1,y_1)[/tex] is the ordered pair for the point you are given and m is the slope.
Here, you would write [tex]y-8=-3(x-7)[/tex]. Then, you simplify to get to slope-intercept form, which is [tex]y = mx+b[/tex], where b is the y-intercept.
[tex]y-8=-3(x-7) \\ y=-3x+29[/tex]
The correct answer is A.