39/78 = .5 = 50%
...................
Square root is this 4 and -4 are square roots to 16 because 4^2= 16
I think 53.088 is the answer
a) 
because it is equal to the area of the shaded region between X=4 and X=6, and the probability that X falls within some interval is given by the area under the PDF.
b) 
because the shaded region is a rectangle of height 1/5 (by virtue of X following a uniform distribution over the interval [2, 7], which has length 5).
