Write a real life problem using A + 3

I would assume you are talking about writing a word problem enforcing the equation A + 3.

In that case, here is my example:

Sophie's parents pay her an average allowance of 4 dollars. Whenever Sophie does extra work, her parents give her an extra dollar, to add to her original allowance of 4 dollars. Sophie does extra work on 3 days. How many dollars does she earn in total?

We can apply the property A + 3, because Sophie gets and extra dollar 3 days.

Solution:

Sophie is getting paid 3 dollars. We simply add 4 to find our answer of 7 dollars.

I am "A" years old. My brother is "A"+3 years old. If "A" is 100, then what is my brother's age.