Answer:
a)

c)
Gavin earned $275
Seiji earned $250
Explanation:
a) Denoting s as the earning of Seiji and g the earnings of Gavin, we know they together earned $525. This forms the equation
s+g=525, or equivalently

We also know that Gavin earned $25 more than Seiji. It can be written as
Combining both equations we get the system

b) The graph is shown below
c) Both functions have one point in common. It's the solution of the system. We can conclude that
Gavin earned $275
Seiji earned $250