Which statement best explains whether y = 3x + 5 is a linear function or a nonlinear function?

Y = 3x + 5 is a linear function because the exponent of x is 1.

In a line formula, the biggest exponent of x in standard form represents how many times the line changed direction.

For example if the equation was y = 4x + 4x^4 + 5 - 2x^2 + 6x^3 (I know it's a long one), then the line changed direction 4 times because the biggest exponent of x is 4.

Or we can use it vice versa, which would be "If the graph changed direction 4 times..." or they gave you a graph and line changes direction 4 times; then the equation has to have a maximum x exponent of 4.

In this case, we have an exponent of 1 which makes the line a straight one. And we call straight lines on a graph "linear".