Approach 1:

You can directly mark the answer as 25 $\times$ x = 20 $\times$ 5 $\Rightarrow$ x=4
Proof:
Observe that
ac = 25 sq units ....(1)
bc= 20 sq units ... (2)
ad = 5 sq units ... (3)
Dividing (1) by (3), we get: $\frac{c}{d}$ = 5 units ... (4)
Dividing (1) by (2) we get $\frac{a}{b}$ =5/4 units ... (5)
​St Multiplying (4) and (5) we get:
Sit $\frac{ac}{bd}$ = $\frac{25}{4}$ sq units
Since its already given that ac = 25 sq units, therefore the missing area 'X' =4 square units.
Approach 2:
Use the simple number approach to break up the values in each cell as shown below 

thus x=4x1=4