In the algebra section, we looked at how we can use letters as numbers and how to find their values. There are times, however, when life gets a little harder:
x + y = 25
We cannot say what x and y are in the equation above because there are an infinite number of possibilities:
x = 1, y = 24
In general, a single equation with two unknowns (we don't know x and y in this case) cannot be solved. What we need is a second equation involving at least one of the unknown variables.