Factor 81-y4, x4y8-100, and 25q8r4-121

please help and if you could show work

All of these are the differences of squares, so use the rule for factoring the difference of squares on each of them.

81-y4
(9 + y2) (9 - y2)
The expression in parentheses on the right is another difference of squares, so factor again:
(9 + y2) (3 + y) (3 - y)

x4y8-100
(x2y4 + 10) (x2y4 - 10)

25q8r4-121
(5q4r2 + 11) (5q4r2 - 11)