Just do pythagorean theorem. The answer is the square root of 75

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.
Answer:
625
Step-by-step explanation:
1. parenthesis first, so it simplifies to ((6+(8)2÷4*1)/2)^4
2. pemdas says that multiplication and division go before addition and subtraction, so ((6+(8)2÷4*1)/2)^4 becomes ((6+16÷4*1)/2)^4 ---> ((6+4)/2)^4
3. then simplify inside of the parenthesis, so it becomes 5^4, which is 625