Fix website errors

this error is appearing on my website

Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/memento1/public_html/amani-photo.com/wp-includes/wp-db.php:1785 Stack trace: #0 /home/memento1/public_html/amani-photo.com/wp-includes/wp-db.php(724): wpdb->db_connect() #1 /home/memento1/public_html/amani-photo.com/wp-content/plugins/query-monitor/classes/QM_DB.php(36): wpdb->__construct('memento1_amani', 'ae3okY!.Tej@', 'memento1_amani', 'localhost') #2 /home/memento1/public_html/amani-photo.com/wp-content/plugins/query-monitor/wp-content/db.php(74): QM_DB->__construct('memento1_amani', 'ae3okY!.Tej@', 'memento1_amani', 'localhost') #3 /home/memento1/public_html/amani-photo.com/wp-includes/load.php(549): require_once('/home/memento1/...') #4 /home/memento1/public_html/amani-photo.com/wp-settings.php(124): require_wp_db() #5 /home/memento1/public_html/amani-photo.com/wp-config.php(71): require_once('/home/memento1/...') #6 /home/memento1/public_html/amani-photo.com/wp-load.php(50): require_once('/home/memento1/...') #7 /home/memento1/public_ in /home/memento1/public_html/amani-photo.com/wp-includes/wp-db.php on line 1785