The tree is vertical, at 90° to its horizontal shadow. The tree's length and its shadow form two sides of a right-angle triangle. If we draw in the hypotenuse, it would make an angle of 25° with the horizontal, since that is the angle of the sun above the horizon. The length of the shadow is the adjacent side, and the height of the tree is the opposite side.
So we have,
tan (25°) = opp / adj = height of tree / length of shadow
From this, you can solve for the height of the tree, and use your calculator to find the tangent for a numerical answer.