Look at each outer number pair:
Top: 2 × 5 = 10
Top right: 3 × 5 = 15
Right: 4 × 5 = 20
Bottom right: 5 × 5 = ? → ? = 25
So, the missing number is 25.
Top: 2 × 5 = 10
Top right: 3 × 5 = 15
Right: 4 × 5 = 20
Bottom right: 5 × 5 = ? → ? = 25
So, the missing number is 25.