$6-)$ Cold air with a mass flow rate of $15k$g$/$s is to be heated steadly from $10C$ to $80C$ in on insulated heat exchanger at $300C$ and leaves at $120C.$ Assuming constant spesific heats Determine

$$ The mass flow rate of hot waste air $($kg$/$s$)$

$$ Heat transfered from the hot air $($kw$)$