Let $P\left(x\right)$ be a polynomial such that when $P\left(x\right)$ is divided by , the remainder is 99 and when $P\left(x\right)$ is divided by $\left(x-99\right)$, the remainder is 19. The remainder when $P\left(x\right)$ is divided by $\left(x-19\right)\left(x-99\right)$ is