How to Hide the "Lp Reading Time" Admin Menu

function plt_hide_lp_estimated_reading_time_menus() {
	//Hide the "Settings → Lp Reading Time" menu.
	remove_submenu_page('options-general.php', 'lp-ert-options');
}

add_action('admin_menu', 'plt_hide_lp_estimated_reading_time_menus', 11);

Where do I put this code?