Please solve this:

A cylindrical tank has a base with a area of 4.(3)^(1/2) meters and an equilateral triangle painted on the interior side of the base. A grain of sand is dropped into the tank, and has an equal probability of landing on any particular point on the base. If the probability of the grain of sand landing on the portion of the base outside the triangle is 3/4, what is the length of a side of the triangle?


a. 4
b. 2
c. 3^1/2
d. 1/2
e. 2/3