Well using the sine rule I get an answer of 210m like you
Let the observation tower be angle C and the fires at 32.6 degrees and 42.5 degrees be A and B respectively. Drawing a perpendicular line down from C we get the height of the tower known to be 135m and two triangles. Call the point where this perpendicular line intersects the line AB as point D.
Thus we have two triangles: CAD and CBD. Since a triangle's angles always add to 180 degrees then it's easy to find the other two angles to be 57.4 and 47.5 respectively.
Sine rule: - this uses the convention that side a is opposite angle A and so on.
For triangle CAD:
(135=CD = the height of the tower)
(I am leaving my answers in trig form to avoid rounding errors at this stage)
For triangle CBD:
The length is given by
See attached for diagram (I scanned it, hence the very unimaginative title): Attachment 18891