A Valentine’s Day Love Story

A teenage boy smitten with a teenage girl in his high school freshman class makes his feelings known. Overjoyed at finding them reciprocated, he took a pen knife to a young hardwood tree in the vicinity and carved their initials within a heart five feet up on the tree’s trunk, as boys will do.
They go back 28 years later. If the tree had added 35% to its height in the first fifteen years of his absence, 10% in the following five years, and two and a half percent in each of the ensuing eight years, how far up the trunk did they have to look to find the carving with their initials?