It tells us that a toy has a mass of 3.0 kg, with a speed of 4.0 m/s.
We apply the following formula:
Ec = m * v²/2
We replace data and solve:
Ec = 3.0 kg* (4.0 m/s)²
Ec = 3.0 kg* 16 m²/s²/2
Ec = 48 kg * m²/s²/2
Ec = 24 kg * m²/s²
Ec = 24 N * m ========> Joules units
Ec = 24 J
The new cartia of the cart would be of 24 joules.