How to solve the attic portrait puzzle in MADiSON

gamepur.com:

There are many twists and turns that you must take to solve the puzzles in MADiSON. One of the more difficult and time-consuming of these puzzles is the attic portrait puzzle. To solve it, you will need to progress through the game a ways to get your hands on all the necessary items. You will also need to do some math. Get your calculator ready, it’s time to solve a puzzle.

The first step to solving this puzzle is obtaining all of the necessary portraits to complete it. When you first enter the attic, you will be able to get two of the portraits. One will be on the wall already and the other will be in the corner opposite where the ladder to get into the attic is. For the other two, you will need to solve a puzzle and complete more of the story.

After progressing a little farther into the game, you will find be able to go through the door near where the TV is located in the small living area. During this part, the statue of Mary will noticeably be gone and will reappear in the hallways. Go through the hallways and follow the path to the back past the projector and the shelves to find the study/office. Here, you will find one of the portraits on the wall.

The last portrait is found in grandpa’s bedroom. Collect the medallions needed for the solar medallion puzzle and complete the puzzle by putting them into the correct position on the wall in the bedroom. This will open a sliding wall nearby. Use the hammer to pull the nails out of the boards blocking the closet and grab the final portrait off the floor.

There is a note that you can find as soon as you enter the attic. This note is pictured in the image below and gives you the hint of adding and subtracting.