上个月，瑞秋省下了 $90 并花掉了其余的零花钱。如果她将支出增加 40%，她的储蓄就会减少 20%。 她的零花钱是多少？ 答：$ ___

1. Calculate the decrease in savings.

$\text{Decrease in savings} = 20\% \times \char36{}90 = \frac{20}{100} \times 90 = \char36{}18$

2. Equate the decrease in savings to the increase in spending.

Since her pocket money remains the same, the increase in spending must equal the decrease in savings.
$40\% \text{ of spending} = \char36{}18$

3. Calculate the original spending.

$\text{Original spending} = \frac{18}{40\%} = 18 \div \frac{40}{100} = 18 \times \frac{100}{40} = \char36{}45$

4. Calculate the total pocket money.

$\text{Pocket money} = \text{Savings} + \text{Spending} = \char36{}90 + \char36{}45 = \char36{}135$