Brainliest + ! can you show me the proper calculation for this? since i got it wrong?

  Well the reason your answer is 15 is because, mode is described as the value in the data that occurs most often. Meaning if 50% of students said that they started school at 15, then that is the value that occurs most often in your data.

if you are saying purchasing 3 social media ads and one newspaper ad counts as one purchase then there are:

6 purchases

if you are asking how many of each then:

18 social media ads

6 newspaper ads