Suppose $6\;kg$ of salt contains $6 \times 10^7$ crystals. How many crystals are there is in $7\;kg$ of salt.

Question

$\begin{array}{1 1} 7 \times 10^7 crystals \\ 7 \times 10^6 crystals \\ 7 \times 10^5 crystals \\ 7 \times 10^4 crystals \end{array} $