Given that,
Mass of object, m = 55 kg
Mechanical energy of the object, M = 4306 J
Potential energy, P = 2940 J
We know that the mechanical energy is the sum of kinetic and potential energy such that,
Mechanical energy = kinetic energy + potential energy

Kinetic energy is given by :
v is velocity of object

So, the velocity of object is 7.04 m/s.