C++ delete a pointer (free memory)

The behaviour of your program is undefined. You can only use delete on a pointer to memory that you have allocated using new. If you had written

int* b = new int;
*b = 10;
int* c = b;

then you could write either delete b; or delete c; to free your memory. Don't attempt to derefererence either b or c after the delete call though, the behaviour on doing that is also undefined.

The confusing part is that the answer to your question

Am I correct to understand in the last line, delete b and delete c are equivalent"

Is yes, they're equivalent, and both UB as mentioned everywhere else here.