Answer:
I have made it in above picture hope it helps
 
        
                    
             
        
        
        
You list the multiples of both numbers and see which number they share that is on each table
For example,
3,6,9,(12),15,18,21,(24)
4,8,(12),16,20,(24)
12 is the least common multiple of the numbers 3 and 4
        
             
        
        
        
Angle b is 4 bro the answer is there in the question
        
             
        
        
        
There are two ways to do this. One is by adding up the squares, which takes a while. The other way is if you notice that the length along the bottom is the same as that long the top, and the same is true for the sides. While it does not appear this way at first, imagine that that was the floor plan of a house. If you looked at it from the side, you wouldn't see the dent in the corner, only one side. Since the length of the top is 13 units, from -7 to 6, and the side is also 13 units, from -6 to 7, the answer is 

52 units long.