The first problem is to push from the back to the front. If the highest bit of plain code after one encryption is X, then:

X*3+1 = 2, or x*3+1 = 22, or x*3+1 = 22, then the solution is X = 7.

Let the highest source code be y, then:

Y*3+1 = 7, or y*3+1 = 17, or y*3+1 = 27, then the solution is Y = 2.

Similarly, the last three digits are 009.

Clear the code of 2008.

The second question, 9 grids, each grid has three possibilities, so the ninth power of 3 = 19683.

The third problem is that the length of the intersection of the hypotenuse and the square is x.

According to similar triangles, there are: (10-4)/x = 10/4, and the solution is x = 2.4, then the area of the square except the overlapping part is

s=(4-2.4)*4/2 =3.2

Question 4: Let the current speed be X and the ship speed be Y;

80/(y+x) + 48/(y-x) = 9

64/(y+x) + 96/(y-x) = 12

List the equations and solve them yourself.

Question 5: Let the amount of grass on the original grassland be m, the growth rate be x, and the amount of grass eaten by each cow every day be y:

m+20x = 10*20*y.................( 1)

m+ 10x = 15 * 10 * y..................(2)

Get x/y = 5

In other words, the growth rate of grass is five times that of a cow every day, so at least five cows can be released.

Question 6: Where is the map?