Answer:
3485 ft
Explanation:
The height above the radar station is found using ...
height = distance × sin(angle)
height = (4200 ft) × sin(55°) ≈ 3440 ft
Since the radar station is 45 ft above the ground, the height of the clouds will be an additional 45 ft:
3440 ft + 45 ft = 3485 ft . . . . height of clouds
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Comment on units
You need to be a bit careful here because one dimension is given in feet and another in yards. You need to use 1 yard = 3 feet to figure that 1400 yards = 4200 feet. You could convert 45 ft to 15 yards and report the cloud height in yards. That would not be wrong, but it would be unusual.