Answer:
155bpm + 20bpm = 175bpm.
Explanation:
Both Ashley and Jonelle will still be in their THR zone.
Ashley's 175bpm is still within the 146bpm - 181bpm THR zone.
Jonelle's 175bpm is also still within the 151bpm - 184bpm THR zone.
Ashley's 155bpm can be added a maximum of 26bpm to still remain within her THR zone while Jonelle's 155bpm can be added a maximum of 29bpm to still remain within his THR zone. Beyond those numbers, their heart rates will exceed their THR zones.