Frequency of a wave =
(speed of the wave) divided by (wavelength)
or
(1) divided by (period of the wave) .
Period of the wave =
(wavelength) divided by (speed of the wave)
or
(1) divided by (frequency of the wave) .
By definition;
M = fo/fe
Where,
M = Angular magnification
fo = Focal length of objective lens
fe = Focal length of eyepiece lens
From the information given;
M = 180/30 = 6
Can you give more description ??