The interquartile range (IQR) is 20
You find this by subtracting the values of Q3 and Q1
Q3 is the right most edge of the box which is 45
Q1 is the left most edge of the box which is 25
IQR = Q3 - Q1 = 45 - 25 = 20
Side Note: The median is not 45. The median is actually 40 since this is the middle line of the box, which is in between 35 and 45