It is convenient to start with the 2-point form of the equation for a line.
... y - y1 = (y2 - y1)/(x2 - x1)×(x - x1)
Either point can be (x1, y1), and the other can be (x2, y2). If we take them in order, we get
... y - 4 = (16 - 4)/(5 - 3)×(x - 3) . . . . . fill in the two points
... y = 12/2(x -3) +4 . . . . . . . . . . . . . . add 4, simpliffy a bit
... y = 6x -18 +4 . . . . . . . . . . . . . . . . . eliminate parentheses
... y = 6x -14 . . . . . . . . . . . . . . . . . . . . put in slope-intercept form