The problem asks us to find the value of $6400 \times 2.7$, given that $64 \times 27 = 1728$.

1. Problem Description

The problem asks us to find the value of $6400 \times 2.7$, given that $64 \times 27 = 1728$.

2. Solution Steps

We can rewrite the expression $6400 \times 2.7$ as follows:

$6400 \times 2.7 = (64 \times 100) \times (27 \times 0.1)$

$6400 \times 2.7 = 64 \times 27 \times 100 \times 0.1$

$6400 \times 2.7 = 64 \times 27 \times 10$

We are given that $64 \times 27 = 1728$, so

$6400 \times 2.7 = 1728 \times 10 = 17280$.

3. Final Answer

The number that should replace the question mark is 17280.