How to partition variance in SAS

Hello everyone,

I have been given a question in answering which, using SAS, I have to calculate the variance in the dependent variable that is accounted for by four independent variables "jointly", "separately, without the presence of the other independent variables" and "separately WITH the presence of other independent variables".

I have a little bit of a hard time distinguishing between these three, esp. the last two. Also, I want to calculate that using SAS.

Thanks in advance