Answer:
0.2 x 10⁻⁴
Step-by-step explanation:
The problem here is to evaluate: 
 (1.8 x 10⁻²) ÷ (9 x 10²) 
To solve this problem, some certain rules of indices must be followed. In the event that we have an expression such as: 
 (a x bˣ ) ÷ (c x bᵃ) = 
 x bˣ⁻ᵃ
 x bˣ⁻ᵃ
 So; 
 (1.8 x 10⁻²) ÷ (9 x 10²) = 
 x 10⁻²⁻²
 x 10⁻²⁻² 
 = 0.2 x 10⁻⁴