What about the Ph.D. in Mathematics, page 6 1 of the first volume of the textbook for the fifth grade of primary school?
The question of the doctor of mathematics:
Area of two squares and area of -2 triangles = = shadow area
8x8+6x6= 100
8x8÷2=32
(8+6)x6÷2=42
100-32-42=26