B E W A R E !! JOSGARITHMETIC's equation, above, will NOT give you the correct value for the rectangle's length.
Hence, width will also be INCORRECT!
Let L be the length, in feet; then the width is 4L-25.7 feet.
Write equation for the half of the perimeter as you read the problem
L + (4L - 25.7) = 14.8 feet ( where 14.8 = 29.6/2 )
Simplify and find L
5L = 14.8 + 25.7
5L = 40.5
L = 40.5 / 5 = 8.1.
Thus the length is 8.1 feet; the width is 4*8.1-25.7 = 6.7 feet. ANSWER
CHECK. The perimeter is 2*(8.1+6.7) = 2*14.8 = 29.6 ft. ! Precisely Correct !