Respuesta :

x= width
length= 3x-7
Area: (x)(3x-7)=40
= 3x^2-7x=40
= 3x^2-7x-40=0
Factorise the equation: (3x+8)(x-5)=0
x=-8/3 (reject because width cannot be negative) or x=5
so width is 5cm and length is 3(5)-7= 8cm !