Let the amount he would have spent without the sales be x. Now, if there is a 65% discount, what this means is that he is exactly paying for 100 - 65% = 35%
Now, it is this 35% of X that is equal to the amount he paid
Thus, mathematically, we have the following;
35/100 * x = 15.60
35x = 15.6 * 100
35x = 1560
x = 1560/35
x = $44.57
This means that without the sales discount, he would have paid $44.57
