510 would be your answer. I hope this helped! :)
Answer:

Step-by-step explanation:
we have
-----> equation A
----> equation B
we know that
The solution of the system of equations is the point 
so
The solution of the equation
is equal to the x-coordinate of the solution of the system of equations
therefore
The solution is 
Given the equation y = kx
Also given that she:
earned $350 after working 40 hours
y = how much earned
x = number of hours
Plug it in
y = kx
350 = k(40)
divide both sides by 40 to find out how much k is
8.75 = k
k = 8.75 so your answer is A.) 8.75
Hope this helps :)