Answer:

Explanation:
Let's start by calling your age
. We know that your brother is 3 years older than you, so we can represent his age as
.
Now, we want to figure out how old your brother was last year. To do this, we need to subtract 1 from his current age. So, we get:

We can simplify this by subtracting 1 from 3, which gives us 2. So, we can rewrite the equation as:

This tells us that your brother was
years old last year.
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Example
To give you an example, let's say you're 15 years old. Then, your brother is 18 (because 15 + 3= 18).
Last year, your brother's age was:
18 - 1 = 17
So, when you were 15 and your brother was 18, your brother was 17 years old last year.