f(x) = (3/4)ˣ - 4
As x gets really negative (3/4)ˣ grows positively without bound (because it's (4/3)⁻ˣ and 4/3 > 1).
As x gets really positive (3/4)ˣ tends to zero but never quite gets there.
So (3/4)ˣ > 0 for all x
So f(x) > 0 - 4 for all x
Answer: { y | y > -4 }, first choice

1) Let's write out both expressions subtracting 4m²+2mn+8n² from 2m²+6mn+2n²

2) Note that when we subtract 4m^2 + 2mn + 8n^2 from 2m^2 + 6mn + 2n^2 we need to swap the sign by placing -1 outside the parentheses and then combine like terms adding those terms algebraically.