You've given the answer, right there in your question.
The "magnitude of gravity" is described in terms of the acceleration due to it, and you just told us what that is.
We can also notice that the figure you gave is about 0.66 of the acceleration due to gravity on the Earth's surface. That tells us that the distance from the Earth's center at that height is about
(1 / √0.66) = 1.23 times
the Earth's radius, so the height is about 910 miles above the surface.
