the temperature T °C inside a house at a time t hours after 6.00 am is given by T=18-4cos(pi t/12) for 0\leqslant t\leqslant 24

the temperature \theta °C outside a house at time t hours after midnight is given by \theta =11-6cos(pi t/12) for 0\leqslant t\leqslant 24

if the difference between the inside and outside temperatures can be represented by D=T-\theta , sketch the graph of D. determine when the difference between inside and the outside temperature is less then 6°C.

guys anyideas?