Simple math. But don't confuse the km and knots!
The closure speed is 120 plus 450 knots = 570 knots = 1026 km/hr = 17.1 km/minute = 0.285 km/sec.
Inflight viz is 4 km. At 0.285 km/s, we have a reaction time of 4 / 0.285 = 14 seconds.
That's of course assuming the avoiding action itself will take zero seconds and that you were looking at the target as and when it came into view, and recognised it for what it was.
Bit of an academic question really.