14.81%
Let's consider there are zero students who enrolled nothing (because the question asked the minimum) and x = the amount of students who enrolled both History and English.
x = (14 + 17) - 27
x = 31 - 27
x = 4
Now, we can easily calculate the number of students who enrolled in both History and English by percentage. Let's consider that y = the number of students who enrolled in both History and English by percentage.
y = 4/27
y = 14.81%
The number of students who enrolled in both History and English by percentage is 14.81%