Answer:
C.) 50%
Step-by-step explanation:
Let the function that represents the given graph is,

Where, x represents the time in years,
y represents the enrollments after x years,
By the graph,
if x = 0, y = 15,

Now, if x = 2, y = 35,

∵ In the exponential function 
b is the growth ( > 1 ) or decay( < 1 ) factor.
Thus, growth factor of the function that shows the given situation is 1.5 ( approx )
Now, growth rate = growth factor - 1
= 1.5 - 1
= 0.5
= 50%
Hence, the percentage rate of growth is 50%.
Option 'C' is correct.