For f (x) = x2 + 8x + 7, evaluate f (x + 4) - f (x). Simplify.

Substituting, we have

... f (x+4) = (x+4) ² + 8 (x+4) + 7

... = x² + 8x + 16 + 8x + 32 + 7

... = x² + 16x + 55

Subtracting the original, we have

... f (x+4) - f (x) = (x² + 16x + 55) - (x² + 8x + 7)

... f (x+4) - f (x) = 8x + 48