Fill in each slot in the square with variables a, b, c, d, and e, in order from left-to-right, top-to-bottom. In a magic square, the sums across rows, columns, and diagonals all add up to the same number called the magic sum.
The magic sum is -3.9, since "diagonal 2" (bottom left to top right) has all the information we need:
3 + (-1.3) + (-5.6) = -3.9
Use this to find the remaining elements
a + b + (-5.6) = -3.9
c + (-1.3) + d = -3.9
3 + e + 0.02 = -3.9
a + c + 3 = -3.9
b + (-1.3) + e = -3.9
(-5.6) + d + 0.02 = -3.9
a + (-1.3) + 0.02 = -3.9
You will find
a = -2.62
b = 4.32
c = -4.28
d = 1.68
e = -6.92