R = Point(yAxis)
P = (0, 80)
f'(x, y) = (0.03 * (y(R) - y))
r: y = y(R)
Steigungsfeld = SlopeField(f')
kurve = SolveODE(f', x(P), y(P), 60, 0.1)
lsg = Locus(f', P)