It is given in the question that,
A 18 inch string is cut into two where the second piece is 3 inches longer than twice the first.
Let the length of the first piece be x inch.
So length of second piece is
[tex](2x+3)inch[/tex]
And total length is 18 inch. That is
[tex]x+2x+3 =18 \\ 3x+3 = 18 \\ 3x = 15 \\ x =5[/tex]
So the length of the first piece is 5 inch and the length of second piece is
[tex](2*5 +3) = 13 inches[/tex]