I have done (a)(b)(c) but fail to do (d). The book's answer of (d) is 67.2 degree.

Three points A, B and C on horizontal ground are such that AB = 10m, BC = 21m and

. The point P lies on BC and

degree. Calculate

(a) the length of AC

(b) the length of AP

A vertical pole VA of height 19m is placed at A. Calculate, to the nearest tenth of a degree, the acute angle between

(c) VB and the horizontal

(d) the plane VBC and the horizontal

Here's my working of (d) but my answer is wrong.

let VB = a , VC = b

consider triangle VBC,

let VX be the height of triangle VBC and VX perpendicular to BC,

angle between VBC and the horizontal =

degree (wrong)

Thanks in advance!