Let x = the amount originally in Victoria's wallet. Every time that she spends money on something, we need to subtract. When she is given money by someone else, we add. So we have:
x - 8 - 7 - 13 + 10 - 15 = 12 (12 is how much she has left after all of her spending and the gift from her brother)
x - 33 = 12
x = 45
Victoria originally had $45 in her wallet