If an x-ray machine emits em radiation with a wavelength of 1.2 x 10 square -11 what is frequency?

I'm not sure what you mean by  1.2 X 10 square -11 and you didn't state the units.

Let's say the wavelength = 1.2 X 10^-11 cm then we calculate frequency:
frequency = c / wavelength
where "c" is the speed of light 299,792,458 meters / second
and the wavelength should be in meters

frequency = 299,792,458 meters per second / 1.2 X 10^-13 meters
frequency = 2.4983e+21 Hertz = 2.4983e+15 MHz

Source:http://www.1728.org/freqwave.htm