The inverse function is one-to-one, find a formula for the inverse. (if anyone could explain how to find this mystical formula, that would be great! )

Given a binomial distribution variable with n=20 and p=0.60 find the following possibilities using the binomial table a) p(x < 13) b) p x > 15) c) p(x = 17) d) p(11 < x < 14) e) p(11 < x < 14)