Propose a molecular formula for a compound that exhibits the following peaks in its mass spectrum.

a) (M)^+• at m/z = 72, relative height = 38.3% of base peak

(M+1)^+• at m/z = 73, relative height = 1.8% of base peak

b) (M)^+• at m/z = 68, relative height = 100% (base peak)

(M+1)^+• at m/z = 69, relative height = 4.3%

c) (M)^+• at m/z = 54, relative height = 100% (base peak)

(M+1)^+• at m/z = 55, relative height = 4.6%

d) (M)^+• at m/z = 96, relative height = 19.0% of base peak

(M+1)^+• at m/z = 97, relative height = 1.5% of base peak