candle b has a height of 280 - 5t, when it comes out of the mold then t=0 so the initial height of b is 280
candle b's height drops by 5 every hour (that's what the -5t part means)
candle a started at 216 and dropped to 192 in 3 hours, so it dropped by 24 in 3 hours so it drops 8 each hour
so candle b starts out taller (280 v. 216) and candle b burns slower (a at 8 per hour and b at 5 per hour), so b will never 'catch up' with a... candle a will be burned out while candle b is still burning
