The marks of 400 candidates are given as a 'less than' table — less than 20: 40, less than 40: 120, less than 60: 260, less than 80: 360, less than 100: 400. Estimate the upper quartile, that is the mark above which the top 25 percent of the candidates lie.

The top 25 percent are the top 100 candidates, so the upper quartile sits at position $3n/4=300$. The cumulative counts 260 and 360 show that the 300th candidate lies in the class 60–80, where $l=60$, cf = 260, $f=360-260=100$ and $h=20$. So $Q3=60+((300-260)/100)\times 20=60+8=68$. The boundaries 60 and 80 are the ends of the class the quartile falls in, not the quartile itself, and 75 confuses the NAME of the 75th percentile with a mark — a percentile is a position in the data, while the answer asked for is a score.