In the following number 7384, if 3 is replaced by 7 how much more or less the new number will be?

Question

$\begin{array}{11} (a)\;\text{it would be 40 smaller} \\ (b)\; \text{it would be 40 bigger} \\ (c)\; \text{it would be 400 smaller} \\ (d)\; \text{it would be 400 bigger} \end{array}$