The definition of the tangent function tells you tan(angle) = (300 ft) / (distance to mountain) This equation can be rearranged to (distance to mountain) = (300 ft) / tan(angle)
For the far end of the river, distance to far end = (300 ft) / tan(24°) ≈ 673.8 ft
For the near end of the river distance to near end = (300 ft) / tan(40°) ≈ 357.5 ft
Then the width of the river can be calculated by finding the difference of these distances: width of river = distance to far end - distance to near end width of river = 673.8 ft - 357.5 ft width of river = 316.3 ft
D=546m. r=1.3m/sec. 546m=1.3m/sec(t). 546m divided by 1.3m/sec = t = 420 sec (the meters will cancel out, leaving the answer to just seconds). 420 seconds divided by 60sec/min = 7 minutes.