=( 1/2 fish body+fish tail)+fish tail

= 1/2 fish body +2 fish tail

1/2 fish body = 2 fish tail = 4 * 2 = 8kg.

Fish body = 8 * 2 = 16kg

Fish head = 8+4 = 12kg

Total weight of fish: 16+ 12+4=32 (kg)

Equation: Let the big fish weigh x kilograms, and get the equation according to the meaning of the question:

( 1/2)x + 4 + 4 = x

Solution: x= 16

Weight of big fish: 16+ 16/2+4+4 =32 (kg)