We'll first simplify both sides of the expression to get (simply using the distributive property):

Then, we can simplify a little bit:

To solve for n, we have to isolate it. Let's subtract 3n from both sides to further simplify it:

Then, add 18 to both sides to get the value of n:

And that's your answer. If you have questions on how I got that, feel free to ask!
836 to the nearest hundred is 800 because number under 50 of the last two digits we round it below. Same thing as above 50 we round it up.
599.99
599.98
599.97
599.96
599.95
3 AND 18, the only factors