It looks like you are trying to calculate the square of a number.
From your equation: \[ __^2 = 3.6 \times 3.6 = 12.96 \]
This indicates that the missing value you are looking for is 3.6, because: \[ 3.6^2 = 12.96 \]
If you have any further questions or need additional calculations, feel free to ask!