12. As shown in the figure, a rectangular lawn is divided into three parts. It is known that the second plot is 10 meters wider than the first plot. The area of the second plot is 1000 square meters, the third plot is 4 meters narrower than the first plot, and the area of the third plot is 650 square meters. Therefore, the area of the first plot is ( ) square meters.
【Answer】750
【Analysis】Key point: Skillful area calculation
Let the width of the first piece be $\mathrm{a}$, the second piece $10+\mathrm{a}$, and the third piece $\mathrm{a}-4$; According to the equal width, $1000 \div(10+\mathrm{a})=650 \div$ $(a+4), a=30$; The width equals $1000 \div(10+a)=25$; Then the area of the first piece $30 \times 25=750$