Question 56903
Call the length = x
Call the width = y

You know that x*y = 48
You also know that x = 3y  - 8

Substitute this x in x*y=48 to obtain:

y * (3y-8) = 48

3y² - 8y - 48 = 0
Now solve this for y (delete the negative root)
The rest of the excercise is for you :-)
(hint: y = 4/3 + 4*sqrt(10)/3 )