Explanation:
do you mean
7×10⁵ × 3×10²
as you can see, these are all multiplications. and we can do in a first step the multiplications that combine the factors with the same exponent base or simple constants :
7×3 × 10⁵×10² = 21 × 10⁷
in what format do you need the result ?
21 × 10⁷
2.1 × 10⁸ (standard format)
210,000,000