The perimeter of a rectangle is 56 meters. The ratio of its length to its width is 4:3. What is the length of a diagonal of the rectangle?
I found a post similar to yours - hope this helps!
First, you find the length and width which are 16 and 12. Using the Pythagorean theorem (a2+b2=c2) , you can figure it out. We know A and B, 162+122=c2. Go on further and you get 256+144=c2 then 400=c2 and finally c=20. The diagonal is 20 units.