PRACTICE EXERCISE $7\mathrm{.}2$

The positive $y-$axis $($semi$-$infinite line with respect to the origin$)$ carries a filamentary current of $2$ A in the $-$ ay direction. Assume it is part of a large circuit. Find H at

$($a$)A(2,3,0)$

$($b$)B(3,12,-4)$

Answer: $($a$)145\mathrm{.}8a_{z}m\frac{A}{m},($b$)48\mathrm{.}97a_x+36\mathrm{.}73a_{2}m\frac{A}{m}.$

I have problems with the angles, iI don't know how to get them