Answer
$12kWh$
$43200kJ$
Work Step by Step
First we determine the amount of electric energy used in $kWh$:
$E=(4kW)*(3h)=12kWh$
Now to determine the amount of electric energy used in $kJ$:
$4kW = 4\frac{kJ}{s}$ and $3h*\frac{3600s}{h}=10800s$
Then the energy is:
$E=(4\frac{kJ}{s})*(10800s)=43200kJ$
