You copied something wrong. As it is, it comes out that the older brother is
7.8654599313 and the younger brother is 3.432729966.
I think 27 should be 21.
the product of two brothers' ages is 21.
the older brother is twice and one more than the younger

So
You solve by substituting 2y+1 for x in the first equation,
then solving for y, then substituting what you get for y in
x=2y+1 to find x.
Edwin