Let x = the length of the shorter piece of string.
The longer piece is 3 feet longer than twice the shorter piece.
2x = Twice the shorter piece
2x + 3 = Three more than twice the shorter piece
Thus:
2x + 3 = Length of the longer piece of string
The total length is the sum of both pieces:
x + 2x + 3 = 12
Subtracting 3 on both sides of the equation:
x + 2x = 9
Simplifying:
3x = 9
Dividing by 3:
x = 9/3 = 3
2x + 3 = 6 + 3 = 9
The shorter piece is 3 feet long
The longer piece is 9 feet long