Hey there!
To start, you must first isolate the 5n term so that you can solve for the variable of n.
To do this, subtract 7 from both sides:
5n+7=21
-7 -7
5n=14
Now, divide both sides by 5 to isolate the n term:
5n/5=14/5
You should get a result of n=14/5
Therefore, your final answer should be n=14/5.
To check if the answer is correct, simply plug 14/5 for the variable n in the original equation. If you get a correct mathematical statement when you simplify, the value is correct:
n=14/5
5(14/5)+7=21
14+7=21
21=21
Therefore, n=14/5 is correct.
Hope this helps and have a marvelous day! :)