Explain how you can tell if a function is a linear based on its equation

If a function is linear, that means the degree on the x variable is 1 when solved for y. This means that the exponent on the x is 1. For example:

y²=x
y=√x
y=x^1/2

This is not a linear function because the power on the x function is not 1

x+y=3
y=-x+3

This is a linear function because the exponent on the x is 1.

Any function where the x doesn't have an exponent present, or has an exponent of 1, is deemed a linear function. 

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The answer is: y would equal 3 because if you simplify the equation then it would be y= 3x+9 and if you divide 3x and 9 by 3 it would equal 3. y= 3