Question 540495
width = x
length = x+4

x(x+4)=165
x^2+4x-165=0

Split the middle term such that when you add the split terms you get -4
and when you multiply you get -165
Take the prime factors of 165
3*5*11

3*5 = 15 
you need 4

+15-11=-4

x^2+15x-11x-165=0
x(x+15)-11(x+15)=0
(x+15)(x-11)=0
take the positive value since width cannot be negative

x=11  
length= 11+4=15

Thats how your teacher got 11 & 15

m.ananth@hotmail.ca