-- Prepare test data
declare @table table (seq tinyint, area smallint, page tinyint)

insert	@table
select 1, 300, 0 union all
select 1, 200, 0 union all
select 1, 100, 0 union all
select 1, 400, 0 union all
select 2, 600, 0 union all
select 2, 500, 0 union all
select 2, 300, 0 union all
select 2, 700, 0

-- Do the work (this is the code you run on your computer).
select		t0.seq,
		b0.i * isnull(max(t0.area), 0) +
		b1.i * isnull(max(t1.area), 0) +
		b2.i * isnull(max(t2.area), 0) area
from		(
			select		seq,
					max(area) area
			from		@table
			group by	seq
		) t0
left join	@table t1 on t1.seq = t0.seq and t1.area < t0.area
left join	@table t2 on t2.seq = t1.seq and t2.area < t1.area
cross join 	(select 0 i union all select 1) b0
cross join 	(select 0 i union all select 1) b1
cross join 	(select 0 i union all select 1) b2
where		b0.i + b1.i + b2.i = 1
group by	t0.seq,
		b0.i,
		b1.i,
		b2.i
having		b0.i * isnull(max(t0.area), 0) +
		b1.i * isnull(max(t1.area), 0) +
		b2.i * isnull(max(t2.area), 0) > 0
order by	t0.seq,
		b0.i * isnull(max(t0.area), 0) +
		b1.i * isnull(max(t1.area), 0) +
		b2.i * isnull(max(t2.area), 0) DESC

Seq  Area
---  ----
  1   400
  1   300
  1   200
  2   700
  2   600
  2   500