convert each fraction to the least common multiple of 20, so 3/4 = 15/20 & 1/10 = 2/20, then divide 15 by 2 and you get a little over 7, so the food will last 7 weeks.
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