(Solved): At a restaurant, the density function for the time a customer has to wait before being seated is g ...

At a restaurant, the density function for the time a customer has to wait before being seated is given by \[ f(x)=\left\{\begin{array}{ll} 0 & \text { if } x<0 \\ 1 e^{-1 x} & \text { if } x \geq 0 \end{array}\right. \] Find the probability that a customer will have to wait at least 6 minutes for a table. Give an exact answer (no decimals].