Write down the equation which links energy ($E$), power ($P$), and time ($t$).

A ground-based laser-propulsion transmitter has a continuous power output of $480MW$. Calculate the total energy output of this transmitter if it beams continuously for 7500 s. Give your answer in Joules ($J$) in standard form.

Due to essential recalibration and cooling cycles, the laser transmitter is not active every day of the year. Over a standard year (where $1year=365days$), the transmitter was active for 78% of the year. Calculate the number of days during that year that the laser transmitter was active.