Please explain in simple terms how do I solve for y: 2x + y = 60.

The equation given to solve is 2x + y =
6.

This equation has two variables x and y. To find a
unique value for 'n' variables the number of equations available should be also be
n.

Else we can only treat any one of the variables as a
constant and express the value of the others in terms of that variable. Also, as the
variable we are taking as a constant is not actually a constant, it can change and there
are an infinite number of solutions for all the variables. They would only be related to
each other in some way by the system of equations.

Here 2x
+ y = 6,

Subtract 2x from both sides of the
equation:

=> y = 6 -
2x

For any value of x there would be a unique value for y.
Both the variables can take on an infinite number of values. They would only have to be
related with y = 6 - 2x.