.
Determine whether the equation represent y as a function of x.
Y=70
Yes or no
-----------------------------------------------
It depends on a context.
A function is an object that must be defined.
The function might be defined by a formula.
It also might be defined as a list/a table of values "the argument-the value", or "the input-the output".
An equation is the object that must be solved.
So, "Y = 70" might be a formula, an expression which defines the function.
It also might be the equation which you need to solve.
In this sense it depends on a context.