Two point charges are fixed along a line and separated by a distance \(d\). The charge on the left has magnitude \(+Q\), and the charge on the right has magnitude \(+4Q\). A third point charge \(+q\) is placed between them along the same line at a distance \(x\) from the charge \(+Q\). If the net electrostatic force on charge \(+q\) is zero, what is the value of \(x\)?