How to solve this?

Question

Identify the slope of the line that passes through the points of the parabola given by y = x² + 4x + 3 when x = 0 and x = 4. I know the answer is 8, but I need an explanation.

Answer 1

The question mentions two points: one where x=0, the other where x=4. Since said points are on the parabola, you calculate the associated y values using substitution (for x) in the function definition.

 

Having done that, you can use the slope formula to determine the slope of a line through (x1, y1) & (x2,y2), where the numbers after x or y indicate which point you're working with--i.e. they should be SUBSCRIPTS).