The puzzle involved melted spots on marshmallows, 6.1 cm apart, and the speed of light (.3 gigameters/second). From that, the frequency of the microwave was needed. The hint mentioned Frequency = Velocity/Wavelength, and that times per second is Hertz. Note that a full wave has an up and a down part and a down part, giving a full wavelength of 12.2 cm. Plugging values into the formula, .3 1000000000 m/s / .122 m = 2459016393 Hertz, or 2.46 GHz (gigahertz). On the back of most microwaves is a decal mentioning the frequency of the microwave is 2.45 Gz.