The answer is infinite solutions, but what would i put in the circled box?

  x = 10 - 2y

Step-by-step explanation:

The question is telling you to express x in terms of y. Essentially, you solve the given equation(s) for x.

x can be found from the first equation by subtracting 2y from both sides:

  x = 10 - 2y

When there are infinitely many solutions, either x or y can be arbitrarily chosen, and the appropriate value computed for the other variable.

Here, the answer is telling you "type an expression using y as the variable as needed." That is, y is selected to be the variable arbitrarily chosen, and we need an expression that will tell us the corresponding value of x. The appropriate expression is found by rearranging the equation(s) to "make x the subject". (I call that process "solve the equation for x.")

here is a big fat