Question

The researcher used the line y = 0.4x + 4 to model data when substituted the value of x=14 into this equation what did the result tell her

Answer 1

Alrighty lets see if I can explain this.
The formula is y=mx+b. We already have m, 0.4, which is the slope of the line, and we have b, 4, which is the y-intercept. If you plug in the given value of x, your formula ends up being y=0.4(14)+4 and when we graph that, your end with a straight line across the graph horizontally. If you solve the formula, your answer is y= 9.6
The slope of any horizontal line is 0, as it remains constant.