If a benzene ring has two or more groups on it, it is the most activating group that will determine the position of the next substituted as illustrated below.
Since OH is more activating than ethyl group, it will direct where the next substituent goes (as indicated by the ortho/para/meta chart). The next group being added in this reaction is NO2. OH is an ortho/para director. Since para position is taken, NO2 will go to the ortho position from the OH group.