For this case what you should do is write the following function:
y = (a / b) * 100
Where,
A: amount of successful free throws
B: total amount of free throws
Substituting values we have:
y = (21/30) * 100
The result is:
Y = 70% (as we expected)
Answer:
a rational function that can model the player's free throw percentage is:
y = (21/30) * 100