It's easiest to start with the point-slope form of an equation, [tex]y-y_1=m(x-x_1)[/tex], where m is the slope and [tex](x_1, y_1)[/tex] is the point given.
We have m = 3, [tex]x_1 = 5[/tex], and [tex]y_1 = 10[/tex].
We plug in these values to get
[tex]y-10=3(x-5)[/tex].
We now rearrange to get this into slope-intercept form, [tex]y=mx+b[/tex], by solving for y.
[tex]y=3(x-5)+10\\y=3x-15[/tex]