In a biased coin, the probability of getting a head is 4 times more than that of getting a tail. Two such biased coins were tossed simultaneously such that probability of getting head on one coin and tail on other is 'x'. A bag contains two green balls, 'y' blue balls and 10 red balls. If two balls are picked at random from bag then the probability that both balls are blue is equal to (x - 157/630).