Parentheses really matter. The answer could be:
$${\mathtt{7.8}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{{\mathtt{5}}} = {\mathtt{780\,000}}$$
Or:
$${\left({\mathtt{7.8}}{\mathtt{\,\times\,}}{\mathtt{10}}\right)}^{{\mathtt{5}}} = {\mathtt{2\,887\,174\,368}}$$