Factored binomial joint pmf

Let the random vector $(X,Y)$ have the joint probability mass function $$f(x,y)=\begin{cases}\dbinom{10}{x}\dbinom{5}{y}\left(\dfrac{1}{4}\right)^{x-y+5}\left(\dfrac{3}{4}\right)^{y-x+10},&x=0,1,…,10; y=0,1,…,5\\0,&\text{otherwise}\end{cases}$$ Let $Z=Y-X+10$. If $\alpha=E(Z)$ and $\beta=\operatorname{Var}(Z)$, then $8\alpha+48\beta$ is equal to __________.