3. (10 points) As shown in the figure, two squares with side lengths of 10 cm and 7 cm overlap partially, and the area of the overlapping part is 9 square cm. The difference in the area of the two shaded parts in the figure is ( ) square cm.
A. 51
B. 60
C. 42
D. 9
【Analysis】The area of the large square is $10 \times 10=100$ square centimeters, and the area of its shaded part is $100-9=91$ square centimeters; similarly, the area of the small square is $7 \times 7=49$ square centimeters, and the area of its shaded part is $49-9=50$ square centimeters; then find the difference between the two shaded areas.

【Solution】Solution: $(10 \times 10-9)-(7 \times 7-9)$
$=91-40$
$=51$ (square centimeters)
Answer: The difference in area between the two shaded parts in the figure is 51 square centimeters.
Therefore, the correct choice is: $A$.