Knowing that the demand for wheat is inelastic, if all farmers voluntarily did not plant wheat on 10 percent of their land, then

Since the demand for wheat is inelastic, it means that a change in the price of wheat will result in a smaller proportional change in the quantity demanded.

Since the farmers will decrease their production of wheat by 10% and the demand for wheat will remain practically unchanged, the price of wheat should increase more than 10%, therefore increasing the farmer's total revenue.