In order to build a "beautiful and happy city", the greening and upgrading project in Changsha is in full swing, and a construction team intends to buy two kinds of saplings, A and B.

(1) If you buy x seedlings of the first kind, you will buy (400-x) seedlings of the second kind.

200x+300(400-x)=90000，

Solution: x=300,

∴ Buy 400-300 saplings B = 100,

Answer: If you buy 300 first-class saplings, you will buy 100 second-class saplings.

(2) If at least one seedling A should be purchased, one seedling B (400-a) should be purchased.

200 a≥300(400 a)，

Solution: A ≥ 240.

A: At least 240 A-level seedlings should be purchased.