$($a$)$ Indicate whether the following linear program is an all$-$integer linear program or a mixed$-$integer linear program.

Max $30$x$1+25$x$2$

s$.$t$.$

$3$x$1+1\mathrm{.}5$x$2<=400$

$1\mathrm{.}5$x$1+2$x$2<=250$

$1$x$1+1$x$2<=150$

x$1,$ x$2>=0$ and x$2$ integer

This is a

linear program.