Vectors 3d angle

r1=(1,2,-1) +t(2,2,1)
r2=(-1,-2,3) +s(4,6,-3)

Two lines they intersect, I proved it and found the point of intersection.

Now they want acute angle. I got theta=75.9 book says they get 43.5 now there is a chance that the book is wrong. Can someone try it out?

What I did: find dot product of 2,2,1 and 4,6,-3. Divide by magnitudes to find cos of the angle then inverse that.

I get 43.5 from the dot product of (2, 2, 1) and (4, 6, -3).

$\theta = cos^{-1}(\frac{17}{3\sqrt{61}})$