Constructions 3

in this questiion since circle touches both the line AB and AC, the center of circle will lie on angular bisector of angle CAB. so measure 3cm in compass and try to make a circle having center on this angular bisector, and touching AB and AC.

you have not specified where the point A is?

so if A is the point where circle touches AC then distance of center of circle from point A will be equal to radius i.e. 3cm.