Say you buy a brand new candle from the store, and pretend like its 3 inches tall.
The moment you light it, that candle will still be 3 inches, but as time goes on and on, the wax of the candle is gradually melting and melting. So in other words the wax is getting less and less from its starting measurement of 3 inches. Soon it will be 2 inches then 1 inch and after that, none at all. So by now you should be thinking it is a negative graph because the wax is getting less and less.
You may be wondering if the graph is curved, the answer is no because very soon after you lit your imaginary candle, the fire stabilized and formed into a constant shape that emits constant heat (assuming you don't apply anything extra.)
So we conclude that it is a negative linear graph.
