we have that
A3=8
A1=2
B1=4
so
The formula is
A3=2*4
Explanation
we have that
A3 ----> is the number in the column A and the row 3
A1 ----> is the number in the column A and the row 1
B1----> is the number in the column B and the row 1
Looking at the table
A1=2
B1=4
A3=A1*B1
substitute given values
A3=2*4=8