The first step in this equation is to Subtract 18 from both sides of the equation. 
 
        
             
        
        
        
In order from greatest to least, the ribbons go
7/8 (Green)
3/4 (Pink)
1/3 (Blue)
This because 7 out of 8 is a larger number than 3 out of 4, and 3 out of 4 is greater than 1 out of 3.
        
             
        
        
        
The answer is C. Note that angle C is 180-90-45=45 degrees, so this is a你isosceles right triangle, and it helps if we draw it on a piece of paper. Since  angle B =angle C, AB must be equal to AC=4, and BC=4*\sqrt(2), according to the Pythagorean Theorem.
        
                    
             
        
        
        
5/8+ 2/5
= 25/40+ 16/40
= 41/40
= 1 1/40
The final answer is 1 1/40~