Tom is 4 more than twice andrews age. sara is 8 less than 5 times andrews age. if tom and sara are twins, how old is andrew?

Andrew= 4 yr.old
Sara=12 yr. old
Tom= 12 yr. old
Basically, what I did was guess and check, but there are other ways also. When I came with Andrew's age of 5 and it was pretty close, I went down to 4 years old and that worked perfect because that way both Tom and Sara are 12 years old.

What's the denominator