For this case we must solve the following system of equations:

To solve we follow the steps below:
We multiply the second equation by -3:

Thus, we have the equivalent system:

We add the equations:

We look for the value of the variable "y":

Thus, the solution of the system is given by:

Answer:

Simply divide 61.50 by 3. You should be able to reach the answer that way
317 is the answer you are looking for.
It's a bit hard to explain but I hope this helps