Answer:
2n + 3n equals to 5n in the end, so just set n equal to literally any number :)
Explanation:
Example:
Let n = 1000
2(1000) + 3(1000) = 5(1000)
5000 = 500
Basically, plug in the number and solve on both sides each time. You will know you've demonstrated it if it's equal on both sides