I dont understand why my answer is wrong

Inside Ruby.h i typed :

@interface Ruby : Gem @property(nonatomic) float ruby

//please create a variable under Ruby called ruby

@end

Inside Bling.h i typed :

@interface Bling : Gem Ruby *ruby=[Ruby alloc] init]; // Please create a variable called ruby and assign it the same structure as Ruby//

@end

What is wrong ?

How does the sub class matter? I ve rewatched the videos 2 - 3 times but i still haven't made out the differences in classes. Yes the button shapes and circle rectangle analogy i understand. But i don't understand how the variables created in shape are linked to the variables created in buttons. And what does the linking do compared to no linking. Its not explained with the code.

@interface Gem : NSObject 
@end

@interface Ruby : Gem 
@property(nonatomic) float ruby
@end

@interface Bling : NSObject
Ruby *ruby = [[Ruby alloc] init];
@end