A tree surgeon is finding the height of a tree. She uses a clinometer to find the angle between the horizontal and the top of the tree, measuring ${25}^{\circ }.$ She then walks $6\text{m}$ toward the tree and measures the angle as ${35}^{\circ }.$

Find the height of the tree.

Angles on a straight line sum to ${180}^{\circ },$ so you can find another angle using $180-35$

There are two right-angled triangles in the image. Use the sine rule to find the hypotenuse of either of them, and then simple trigonometry to find the height of the tree.