Answer:
Let the money Seiji got be x and Gavin, y.
Total is 425.
So, x + y = 425
Gavin got 25 more than Seiji.
So, y = x + 25
I will use substitution method.
Substitute y = x + 25 in x + y = 425.
x + x + 25 = 425
2x + 25 = 425
2x = 400
x=$200
So, x is Seiji and he got $200.
For Gavin, substitute x in the equation of y.
y = x + 25
y = 200 + 25
y = $225
So, y is Gavin and he got $225.
For the graph part, I don't know how to show you. Hope you will be able to do the rest by yourself. If you need help with graphing, you may use desmos.com.