Let the price of corn be x, that of wheat be y and that of soybeans be z, then
900x + 540y + 360z = 6930
1125x + 150y + 225z = 5475
860x + 645y + 645z = 8879.50
Solving simultaneously,
x = 3.2; y = 3.5; z = 6
Therefore, the price per bushel of corn is $3.20, that of wheat is $3.50 and that of soybeans = $6