IF statement question

[jengels]

I understand I can write a statement like:

if==12 or if <12 but how do you write an if statement for something like,

A = 90-100
B = 80-89

How do you write the if statement for that?
My java book doesnt tell you how to write an if statement for a number between like 90 and 100.

[AQWst]

if X >= 90 && X<100;
if X >= 80 && X<90;

[jengels]

Thanks for the help!!!