We can use completing the square.We add 16 and subtract 7 to both sides. Now we get m^2+8m+16=9. The left sides becomes (m+4)^2=9. Taking the square root of both sides and subtracting 4 we get -1 and -7.
1/3 (0.333,,,) is 0.05666... away from 0.39 .
2/5 (0.4) is 0.01 away .
3.8 (0.375) is 0.015 away .
9/25 (0.36) is 0.3 away .
2/5 is the closest one.