3。 The sum of three different prime numbers is 82, so there must be 1 prime number =2, and the sum of the other two different prime numbers =80. There are many groups of such two prime numbers, such as 7+73, 13+67, 19+665438. . . However, to make the volume bigger, the bigger the length * width * height, the better. The prime number 2 has been determined, so the product of the other two prime numbers should be bigger, the better. The closer two numbers are, the greater the product is, so the two prime numbers are 43+37 and the volume =43*37*2=3 182.

4。 2*2=4 square decimeter (bottom area) 5/4= 1.25 decimeter water height (volume of poured water divided by bottom area = height) 15cm = 1.5-/kloc-0.