Can some one tell me that :How can i identify the form of polynomial functions in different cases . For example, from the table of value :

(1, 38.4) , (1.5, 30) , (2, 19.6) , (2.5 , 7.2)

How can i know that the function that model this table of value is which one in polynomial function to know the general form of it, like it is a quadratic or .... functions ? Will we need to do some steps to know or we just guess ?

Thank you a lot!