For my sons home work
This is an equation so what ever operation you do to one side you have to do to the other in order to maintain the equality.
So multiply each term by a -1 which then makes the original equation 5x+12=27 now subtract 12 from both sides and you have 5x=27-12 =15. We are getting close now 5x=15 so now we can divide both sides by 5 which gives x=3 or you ca say what number when multiplied by 5 is 15 and the answer is 3.
I hope this helps you help your son.
I used to live on Missouri St in Pacific Beach when I was attending UCSD many years ago. Lots of good memories...