Which number will replace the question mark?

9 3 8 4

4

In 1st figure : 5 × 6 =30, 3 × 10 = 30,  In 2nd figure : 6 × 6 =36, 9 × 4 = 36,  Similarly, In 3rd figure : 9 × 8 = 72, 18 × x = 72, Here, x = \(\frac{72}{18}\) = 4