This is the first puzzle of Hogwarts Escape. You encounter a brick wall which will lead you into Diagon Alley if you just press the right brick.
You are given a ‘start’ brick and from there on you need to navigate through the bricks by going left, right up and down.
Did you notice the carvings on the wall that tell you left = right and up = down?
You have to remember that you don’t go straight up or down. You have to follow the grid of the bricks.
Alright, ask and you will receive. The correct answer here is ‘3.11’.
You start at brick 3.7 and then you go three bricks right downwards, three bricks left, two bricks right up, two bricks left up and three bricks right up.