It's all right there in front of you.
-- The formula for volume is
Volume = (one dimension) x (another dimension) x (the last dimension)
-- The dimensions are (4), (n + 2), and (n + 5).
-- The volume is 280 .
Just multiply the 3 dimensions together, then say " = 280 ",
and solve the equation you have for 'n' .
Hint:
(4) x (n + 2) x (n + 5) =
(4) x (n² + 7n + 10) =
4n² + 28n + 40 = 280
Take it from there. Find 'n' .