ORA-00849: SGA_TARGET cannot be set to more than MEMORY_MAX_TARGET

SQL> show sga
SQL> show parameter memory
SQL> show parameter sga
SQL> create pfile = 'INITPRIM.ORA' from spfile ='SPFILEPRIM.ORA';
File created.

 modify pfile as per your need using some editor, and remove your spfile

SQL> create spfile = 'SPFILEPRIM.ORA' from pfile ='INITPRIM.ORA';
File created.

SQL> STARTUP
ORACLE instance started.
Total System Global Area 3.4206E+10 bytes
Fixed Size                  2256912 bytes
Variable Size            1.9864E+10 bytes
Database Buffers         1.4227E+10 bytes
Redo Buffers              112771072 bytes
Database mounted.
Database opened.