It should be12m! The premise is that the length of the tree is positive, that is, perpendicular to the horizontal line, and the shadow of the tree is in the direction from the root to the slope! Cartography shows that the angle between the sun and the tree is 30 degrees, and the angle between the tree and the slope is 60 degrees, so the shadow of the tree, the tree and the slope form a right triangle (three angles are 30 degrees, 60 degrees and 90 degrees respectively), one of which is 6 meters short, and the height of the tree is equivalent to the hypotenuse on the right triangle, so it is twice as high as 6 meters, and 6× 2 = 12 meters.