I believe you have to get all the like terms on the same side. So since 7m+n is being divided by Q in order to move it to the other side of the equal sign you must multiply each side by Q. Then you would end up with 7m+n=2m(q). 7m and 2m are alike so you then take the 2m and subtract it from each side. So your equation should look like 7m-2m+n=Q. Then combine your like terms and you end up with 5m+n=q