The number of primary, secondary and tertiary amine isomers possible (structural isomers) for the compound with formula ${\mathrm{C}}_4{\mathrm{H}}_{11} \mathrm{N}$ are

Primary amines,

Secondary amines,

Tertiary amines,

So, there will be 3 primary amines, 2 secondary amines and 1 tertiary amines are possible from ${\mathrm{C}}_4{\mathrm{H}}_{11} \mathrm{N}$.