In spherical coordinates, find the value of phi:

rho cos ⁡ ( ϕ ) = z

i f ( x , y , z ) = ( − 3 4 , 1 4 , − 3 2 ) . ϕ = ? ? ?
a. pi
b. (5/6)*pi
c. (2/3)*pi
d. (3/4)*pi