39 x 5 = (30 x 5) + (9 x 5) = 150 + 45 = 195
He did not change the sign of operation when 28 crossed the equals sign. 
        
             
        
        
        
Answer: x = -2
Step-by-step explanation:
 
        
                    
             
        
        
        
Answer:
26 ft and 46 ft.
Step-by-step explanation:
The prime  factors of 42 are 2 * 3 * 7.
Possible lengths and widths  are:
L = 7, W = 6 giving a perimeter of  2*7 + 2*6 = 26 ft.
L = 14 , W = 3  giving perimeter = 34 ft.
L = 21, W = 2 giving perimeter = 46 ft.
 
        
             
        
        
        
Answer:
Rectangular prism- 12 edges
Rectangular pyramid- 8 edges 
Triangular pyramid- 6 edges
Triangular prism- 9 edges
I hope this helps!