Question

the smallest unit in physics is the Planet length.wr need to know constant (h) the speed of light (c) and Newton's Gravitational Constant ( G). Find the Planck Length.

Answer 1

Yes, that's right.  It's the 'Planck' length, not the 'Planet' length.

You could easily find these with a web search.  But in gratitude
for the bountiful 5 points, I've saved you the trouble. 
AND guess what !   By doing that, I learned something, and
you didn't.

Speed of light (c):                 299,792,458 meters per second

Gravitational constant (G):   6.67 x 10⁻¹¹  newton-meter²/kilogram²

Planck's Konstant (h):           6.63 x 10⁻³⁴ joule-second

Planck Length:                      1.6 x 10⁻³⁵ meter
                                            (about 10⁻²⁰ the size of a proton)

Planck Time:                          10⁻⁴³ second
                                             (about the time it takes to travel
                                              a Planck Length at the speed of light)  

Answer 2

Planck length is the going to be the smallest unit of measure known. The speed of light is a constant, the universes speed "limit". Although quantum entanglement beat that speed, but it doesn't threaten the speed of light since the process doesn't hold information. And that was from my own knowledge of the information I soak up daily in college education on the path to a PhD in physics.