Step-by-step explanation:
in what form do we need the equation ?
I assume the most common one : slope-intercept
y = ax + b
"a" being the slope, "b" being the y-value when x = 0 (hence the point, where the line intercepts the y-axis).
we got the slope (a) already, so it equation looks like this so far
y = -3x + b
now we are simply using the x- and y-coordinates of the given point to get "b" :
4 = -3×-5 + b = 15 + b
b = -11
and the full equation for f(x) is
y = -3x - 11
