Mr BBC - Sorry I don't know how to put up diagram - which would have helped greatly.
Anyway: Let T and B be base of building. Let BT = height of building = h
From facts given we can derive 3 right-angled triangles.
1) TBP right-angled at B: angle TPB = 40
2) TBQ right-angled at B: angle TQB = 30
3) BPQ right-angled at P
BP = h/tan 40
BQ = h/tan 30
BQ2 = BP2 + 202
^2 = (\frac {h^2}{tan^2 40})^2 + 400 )
Book answer = 16
Anyway: Let T and B be base of building. Let BT = height of building = h
From facts given we can derive 3 right-angled triangles.
1) TBP right-angled at B: angle TPB = 40
2) TBQ right-angled at B: angle TQB = 30
3) BPQ right-angled at P
BP = h/tan 40
BQ = h/tan 30
BQ2 = BP2 + 202
Book answer = 16
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