A candy company distributes boxes of chocolates with a mixture of creams and toffees. Suppose that the weight of each box is $1$ kilogram, but the individual weights of the creams and toffees vary from box to box. For a randomly selected box, let X and Y represent the weights of the creams and the toffees, respectively, and suppose that the joint density function of these variables is shown below.

f$($x$,$y$)=(1/6)(5$x$+7$y$),0<=$x$<=1,0<=$y$<=1$

Find the probability that in a given box the creams account for more than $1/2$ of the weight.

a$.$

$29/48$

b$.$

$55/64$

c$.$

$13/54$

d$.$

$11/54$

e$.$

$31/48$