Answer:
63 miles per hour 
Explanation:
you just divide miles and hours to get your average speed
 
        
             
        
        
        
Here are the answers to the question. Make sure to give a valid reason, please. 
A. the sum of the protons and neutrons in one atom of the element.
B. a ratio based on the mass of a carbon-12 atom.
C. a weighted average of the masses of an element's isotopes.
D. twice the number of protons in one atom of the element.
 
        
             
        
        
        
First of all, there are not <u>just</u> two applications that are solely applicable to the electron beam welding process. There are MANY.
Please visit out website at the URL below and you can click the "View Application" button under each  listed Industry segment to view case studies of commonly EB welded applications. 
https://www.ptreb.com/electron-beam-welding-applications
And for more general information on our welding process, we have an informational section you can peruse as well:
https://www.ptreb.com/electron-beam-welding-information
Good luck with your assignment-  we are glad to hear they are teaching about EBW in high school!!!
 
 
        
             
        
        
        
Explanation:
Here,
object distance(u)=20cm
image distance(v)=80cm-20cm=60cm
focal length(f)=?
we know ,
(1/f)=(1/v)+(1/u)
1/f = 1/60 + 1/20
1/f = (1+3)/60
60 =4f
f=15cm