posted by johnny .
At what altitude above Earth's surface would the gravitational acceleration be 3.0 m/s2?
I will be happy to critique your thinking.
g = (G*M)/r²
Where G is The gravitational constant, M is the mass of earth, and r is the distance from the center of the earth.
Given this formula, you should be able to calculate the distance (for data about earth's mass and radius, search wikipedia for "Earth" and look in the table on the right)