The 1H NMR spectrum of CH3COCH2C(CH3)3, 4,4-dimethyl-2-pentanone, taken at 300 MHz shows signals at the following positions:

Question:

The 1H NMR spectrum of CH3COCH2C(CH3)3, 4,4-dimethyl-2-pentanone, taken at 300 MHz shows signals at the following positions: 307, 617, and 683 Hz downfield from tetramethylsilane
(a) What are the chemical shifts (() of these signals?
(b) What would their positions be in hertz, relative to tetramethylsilane, if the spectrum were recorded at 90 MHz? At 500 MHz?
(c) Assign each signal to a set of hydrogens in the molecule.