HELP PLZ NEED IT

compute the sum 

$a)[ 101^2 - 97^2 + 93^2 - 89^2 + \cdots + 5^2 - 1^2.]$

compute the sum 

$b)[ (a +(2n+1)d)^2- (a + (2n)d)^2 +(a + (2n-1)d)^2 - (a+(2n-2)d)^2 + \cdots + (a+d)^2 - a^2.]$

PLZ HELP VERY CONFUSING AHHHH