The probability of a transistor failing between $t=a$ months and $t=b$ months is given by $c \int_{a}^{b} e^{-c t} d t,$ for some constant $c$.
(a) If the probability of failure within the first six months is $10 \%,$ what is $c ?$
(b) Given the value of $c$ in part (a), what is the probability the transistor fails within the second six months?