The length of (L) of a simple pendulum is directly proportinal to the square of the time (7).WHIch type of grpah can best describe this relationship?

The words "directly proportional to the square of the time... " holds the key. It means that L and time t have the relationship

L=kt^2

for some constant k.

If we put it into the more generic form y = ax^2 , what kind of graph does that suggest to you?