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.
