Newton Raphson Method?????? HELP!

This is the last question on some tutorial sheets im going through and Im completely lost on this last question....

1) "Show that the problem of finding the cube root of 70 is equivalent to finding a root of (x^3 - 70 = 0). Approximate this root using the Newton Raphson Method. Choose 4 as the initial estimate. Continue the approximation until two successive approximations, rounded to 3 decimal places, are the same."

I will be 1) seriously impressed and 2) very gratefull if anyone can explain this to me.

Thaaaaaanks