If x is the width, then the length is (2x+8).
The perimeter is
x + (2x+8) + x + (2x+8) = 76 centimeters, or
6x + 16 = 76
6x = 76 - 16 = 60
x = = 10 centimeters is the width. ANSWER
Length = 2*10+8 = 28 centimeters. ANSWER
CHECK. The perimeter is 10 + 28 + 10 + 28 = 20 + 56 = 76 centimeters. ! Correct !