Answer:
Each month you should save $ 150
Explanation:
First, the earnings are given per year, so we need to transform $36000/year into dollars per month. So, using a rule of three as following, we obtain:
$ 36,000 ------------- 12 months
X -------------- 1 month
Solving for X, we get:

X = $ 3,000 /month
it means that earn $36,000/year is equivalent to earn $3,000/month
Now, we need to find the 5% of $3,000, this can be calculated making the following multiplication:

Then, each month you should save $150