The number of acres of corn, wheat and oats planted in the first question is x, y, z, y and z respectively;

Second, the number of corn, wheat and oats planted in five 120 mu is X 1, Y 1 and Z 1 respectively, and the number of 25 mu is X2, Y2 and Z2 respectively.

Assuming that corn, wheat and oats are planted in X, Y, Z, Y and Z mu respectively, the maximum income max = 400 x+200 y+250 z. ( 1).

Constraints: In order to obtain maximum benefits, according to the above table,

Science and technology.

0 = & lt3x+y+2.5z & lt； = 1000(2)

0 = & lt0.8x+0.2y+0.3z & lt； =300(3)

0 = & ltx+y+z & lt； =625(4).

Set up 5 plots 120 mu of land, in which X 1, Y 1 and Z 1 are used to plant corn, wheat and oats respectively; If there are three plots of land of 25 mu in X2, Y2 and Z2, and corn, wheat and oats are planted respectively, the maximum income Max = 400 (x1+X2)+200 (y1+Y2)+250 (z1+Z2). ( 1)

Constraints: In order to obtain maximum benefits, according to the above table,

Science and technology.

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Write the rest yourself.