The gravitational acceleration at any distance r is given by

where G is the gravitational constant, M the Earth's mass and r is the distance measured from the center of the Earth.
The Earth's radius is
, so the meteoroid is located at a distance of:

And by substituting this value into the previous formula, we can find the value of g at that altitude:

If the boat is floating, then it's just sitting there, and not accelerating
up or down. That means the vertical forces on it must be balanced.
So if its weight (acting downward) is 100 newtons, then the buoyant
force on it (acting upward) must also be 100 newtons.