You can do anything between .50 and .75. For example .55. .55=55% .55 also equals 11/20 as a fraction
Answer c=12 bellow is a step by step explanation hope it helps
Given that,
= 39
We will find the second term 

Similarly,

Now we use the option checking method,
Suppose we check 4th option
a_{n}= 6n + 33
for n=1
= 6(1) + 33 = 39

It means option D is correct