Their difference in age: $$9-5=4$$  When Mike is $$20$$, Sara is $$20-4=16$$ 
Sara is $$5$$ years old and Mike is $$9$$. How old will Sara be when Mike is $$20$$ years old? 
A. $$16$$ 
B. $$20$$ 
C. $$24$$ 
D. $$28$$ 
E. $$30$$ 