Answer: 24.7 degrees Max
Explanation:
m*g = 3 * 9.8 = 29.4 N. = Wt. of book.


Fp = 29.4*sin A = Force parallel to the
plank.


Fn = 29.4*Cos A = Force perpendicular to
the plank.


Fs = u*Fn = 0.46*29.4*Cos A

Fp-Fs = m*a

29.4*sin A - 0.46*29.4*Cos A = m*0 = 0

29.4*Sin A = 0.46*29.4*Cos A

Sin A = 0.46*Cos A

Divide both sides by Cos A:

Sin A/Cos A = 0.46

Replace Sin A/Cos A with Tan A:

Tan A = 0.46

A = 24.7 degrees Max.