I have the following Data set

naics. 1989. 1990. 1991. 1992.

111 xxxxx xxxxx xxxxx xxxxx
113 xxxxx xxxxx xxxxx xxxxx
112 xxxxx xxxxx xxxxx xxxxx
115 xxxxx xxxxx xxxxx xxxxx
114 xxxxx xxxxx xxxxx xxxxx
212 xxxxx xxxxx xxxxx xxxxx
221 xxxxx xxxxx xxxxx xxxxx
213 xxxxx xxxxx xxxxx xxxxx
214 xxxxx xxxxx xxxxx xxxxx


I need to add specific rows together,

generate a new row (111_112) by adding the values for each year for the 111 and 112

generate a new row (113_114_115) by adding values for each year for 113,114 and 115