A graph with a slope that decreases from left to right is negative. This slope would mean as x approaches +infinity y would approach -infinity and vice versa. So as x increased y would decrease and as x decreased y would increase. This is called an inverse relationship because the values change in opposite ways.
To find the cost before tax, we must find out how much the tax is. So we multiply 252 x .05 to get 12.6. So we know the tax was 12.6 dollars. Now all we have to do is subtract that from the total to get our answer. 252 - 12.6 = 239.4.
