Answer:
1) The third option.
2) The last option.
Step-by-step explanation:
1) f(x) is greater on the interval (0,3), which is opened, because if you substitute
you obtain the following result:

2) If
, you obtain that:

Therefore: 
So perimeter is adding all sides
In this picture, you have all sides, so add them up!
(2a-3)+(3a+1)+(2a) = P
So this expression shows that we're adding all sides that gives us the P, or perimeter :)
Assume the second number is x, then the other two are x - 2, x + 2
So x-2 + x + x + 2 = 51
-> 3x = 51
-> x = 17
The answer is 2.686, and i am writing these extra characters to pass the 20 character qualifications.