To answer the question above, know that one of the way of writing the equation of the line is through the point - slope form which is generally expressed as,
y - y1 = m(x - x1)
where m is the slope and x1 and y1 are the abscissa and ordinate of the point, respectively.
Substituting the given data to the equation above,
y - 5 = -1(x -0)
By simplification we get an answer of
y = -x + 5