How do we tell distance to target at the receiver from frequency modulation?
You ask about FM and then give a constant frequency example.
There is much on web on this.
Envida in a comment cites his own June 2016 SE EE answer here.
This is correct but depending how used you are to the maths may hide the simple truth.
A frequency-swept-with-time signal is transmitted and reflected from the 'target'. On return the reflected signal is mixed with the current transmitted signal and the difference frequency is extracted. This is proportional to distance.
Envida's analysis confirms this key result

Here is a simple example from my experience.
I long ago had an APN-1 radio altimeter.
It used a push pull Acorn tube transmitter and a diode balanced mixer in the receiver front end.
A sniff of transmitted signal was added to the RX mixer.
The TX was modulated with a voice-coil driven electromechanically varied capacitor which changed the TX frequency. The voice coil was driven with a sawtooth wave so that it swept across a frequency range.
Mixing the TX &amp; RX signals in the balanced mixer gave a difference frequency which was proportional to the time taken for the reflected RX signal there &amp; back flight.
From memory max altitude was 20,000 feet with the RX signal being from ground return into a passive mixer - astounding.
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Here is the key part of the circuit diagram:
Balanced mixer at left, Wobbulated transmitter in middle, wobbulator driver at right driving Y101 voicecoil in middle, altitude indicating difference frequency at Anode of V101 exits via C119, C120.

Writeup here
Images here
Full circuit!