A is correct. Here's why:
As the chart shows, a 165cm person with a BMI of 28 is 170 lbs. Since that is considered overweight by the color chart (yellow), he needs to achieve normal (green), which will set him at 150 lbs, 20 of that below what he is currently. He wants to achieve this goal by summer, therefore, he needs to lose 20 lbs by summer