Change Thumbnail Size in Ih Recent Posts

I’m displaying the recent post images on my front page. I need to remove the crop aspect (already turned that off in Settings > Media) and just resize the image to be a specific size every time. I’ve tried to add some code to my functions.php and am getting nowhere.

add_filter( 'image_size_names_choose', 'my_custom_sizes' );
	function my_custom_sizes( $sizes ) {
	return array_merge( $sizes, array(
	'front-books' => __( 'Front Book Covers' )
	) );
}


function white_setup() {
	
	//Register custom thumbnail sizes
	add_image_size('front-books',75,100,false); 
	add_theme_support( 'post-thumbnails' );
	set_post_thumbnail_size(75,100);

}

URL: http://www.goodlandtownshiplibrary.org