Of 60 students, 35 play a sport, and 20 of those 35 also play an instrument. If a student who plays a sport is selected at random, what is…

This is a conditional probability. We are told the student plays a sport, so the sample space is the $35$ sport players, not all $60$ students. Of those, $20$ also play an instrument, so the probability is $\frac{20}{35}=\frac{4}{7}$, choice J. Choice F ($\frac{20}{60}$) divides by all students, ignoring the condition. Choice H ($\frac{35}{60}$) is the probability that a random student plays a sport. Choice G ($\frac{15}{35}$) is the probability that a sport player does not play an instrument, since $35-20=15$.