PLEASE FOLLOW THE DIRECTIONS AND SHOW YOUR WORK. IM OFFERING 15PTS (Way more than its worth) AND BRAINLIEST ANSWER. PLEASE HELP QUICK

I'll take this challenge since I'm not feeling lazy for once....   x would represent Gavin and y would represent Seiji.  

a.  [tex]x+y=425, x-y=25 [/tex]   




b.   I will solve your system using substitution.    
[tex]x+y-425, x-y=25[/tex]  
Step 1: Solve [tex]x+y=425[/tex] for x
[tex]x+y+-y=425+-y [/tex] (add -y for both sides)
[tex]x=-y+425[/tex]
Step 2: substitute [tex]-y+425[/tex] for x in [tex]x+b=25[/tex]
[tex]x+y=25[/tex]
[tex]-y+425-y=25[/tex]
[tex]-2y+425=25 [/tex] (simplify both sides of the equation)
[tex]-2y+425+-425=25+-425 [/tex] (add -425 to both sides)
 [tex]-2y=-400[/tex]
[tex] \frac{-2y}{-2} = \frac{-400}{-2} [/tex]
y=200
step 3: substitute 200 for y in [tex]x=-y+425[/tex]
[tex]x=-y+425[/tex]
[tex]x=-200+425 [/tex]
[tex]x=225[/tex]
[tex]x=225, y= 200[/tex]




c.   Already answered with the picture that is attached.



d.   Gavin earned 225 dollars while Seiji earned 200 dollars.