Well technically this problem is wrong, as two sides are the same on a rectangle on each side. 
 
        
        
        
Answer:
radius = 15ft
diameter = 30ft
Step-by-step explanation:
 
        
             
        
        
        
A)
The question tells us that 
y + z = 180
And 
y=3x+20
z=x
So we put them in the first formula:
y + z = 180
(3x + 20) + x = 180
Add and get x to one side:
4x + 20 = 180
4x + 20 - 20 = 180-20
4x = 160
Divide both sides by 4
x = 40
B)
Put x back in to equation to get size of each angle:
Y =3x +20
Y=3(40)+20
Y=120+20
Y=140
Z=x
Z=40
Verify: y+z=180
140+40=180
180=180
        
             
        
        
        
The correct answer is x = 20
        
                    
             
        
        
        
Cross multiplying we get
x^2 = 2*7x
x^2 = 14x
x^2 - 14x = 0  is the answer