Pls help me, i don't get the question

What number is 7 units left of -15?

If it 8 inch candle burns at 7/10 inch per hour and a 6 inch candle burns at 1/5 inch per hour after how many hours would both candles be the same height

An airplane is flying at an elevation of 5150 ft, directly above a straight highway. two motorists are driving cars on the highway on opposite sides of the plane, and the angle of depression to one car is 35 ̊ and to the other is 52 ̊. how far apart are the cars?