Often times during volcano eruptions the clouds have large static charge buildups that cause lightning to happen. If a rock is ejected by the volcano and it flies to a height of $1905$ m$,$ and the clouds have a charge concentration of $+40\mathrm{.}0$ C at a height of $3600$ m and $40\mathrm{.}0$ C at a height of $1000$ m$,$ what is the electric field at the ejected rock?