Analysis of Structures $-$ #$1$

Classify each of the structures as statically determinate, statically indeterminate, or unstable. If indeterminate, specify the degree of indeterminacy. The supports or connections are to be assumed as stated.

$($a$)$ Unstable

$($b$)$ Stable and statically determinate

$($c$)$ Stable and statically indeterminate to the second degree

Can You please elaborate on the definitions of Stable, Unstable, Statically Determinate$/$Indeterminate$,$ and explain how to determine the degree of indeterminacy.