If you are having issues with decimals, you can rid the decimal by multiplying it by the closest 10th,100th,1000th,etc. place. In this case, just multiply it all by 10. It will become 7n+8n=21. Add the same variables and you should get 15n=21. Divide 15 to both side and n=21/15 and simplify it. N would = 7/5 or 1.4.