Since they each paid the same amount, we can figure out that 9*4=36 dollars is the price of the gift. Next, since there was a 10% discount (or 0.1 by moving the decimal 2 spots to the left), we can say that the original gift price is x and
x-0.1*x=0.9*x due to that we subtract the 10% discount (and it's 10% of the original price). In addition, the sisters paid 0.9*x, which is 36. Dividing both sides by 0.9, we get x=40
