Thinking: Raw water volume: 40× 30×10 =12000 (㎝ 3).

The area of the bottom of the refrigerator after adding iron blocks (volume is not bottom× height, right): 40× 30-20× 20 = 800 (㎝ 2).

Water height (height is the bottom of the roll): 42,000 ÷ 800 =15 ()

A: At this time, the water level is 15㎝.