15 . In a $3 \times 3$ grid, fill in the numbers $1,2,3,4,5,6,7,8,9$ so that the sum of the numbers in any three squares in a row, column, or diagonal is equal.
【Key Point】Magic Square【Difficulty】Comprehension
【Answer】
【Analysis】
$1+2+3+\cdots \cdots+9=45,45 \div 3=15$, the sum of numbers in each row and each column is 15.