Find the sum of the series $\displaystyle 2^2+4^2+6^2+...+50^2$

Using the above result , find the value of $\displaystyle 1^2+3^2+5^2+...+49^2$ .

My working

$\displaystyle \sum^{25}_{r=1}4r^2=22100$

The question says use the above result and this is what i am confused with . How to use the result above to determine the sum of the following series . Is this the method of differences ? If yes , how do i apply ?