Working with average numbers and finding unknown variables?

Question

There is this question I was approached with and I am absolutely stumped on where to even begin to solve it. It goes like this:

Based off the following 4 equations, find the average of $x_1$, $x_2$, $x_3$, and $x_4$.

$$x_1 + \frac{x_2+x_3+x_4}{3} = 25$$

$$x_2 + \frac{x_1+x_3+x_4}{3} = 37$$

$$x_3 + \frac{x_1+x_2+x_4}{3} = 43$$

$$x_4 + \frac{x_1+x_2+x_3}{3} = 51$$

However I'm unsure of how to move on from here or if I am even going in the right direction.

Answer 1

Hint:

Sum the left-hand sides and the right-hand sides of the 4 equations. What do you get?