The problem does not mention the height of S. Mr. Watkins, so we are just going to assume its from his feet.
So, i made this drawing to represent him and the tree, at a distance of 10 meters looking up at a 25* angle.
I marked the opposite side, adjacent side, and hypotenuse.
x is angle where you are "looking" from. I.E., from the POV of mr watkins.
sin(x) = opposite/hyp
cos(x) = adj/hyp
tan(x) = opp/adj
So, we have an unknown side which is the opposite side, represented by length x.
The side adjacent is 10 meters.
The angle from him is 25 degrees.
What deals with adjacent and opposite? Tangent.
Tan(25) = x/10
Solve for x.
10tan(25) is the height of the tree = 4.66
The height of the tree is 5 meters.