$8.$ A production process can make either four units per hour of product $1$ or five units per hour of product $2$ or any combination of the two products. If X$1$ equals the number of units of product $1$ and X$2$ equals the number of units of product $2$ to produce, and there are only eight hours of production time available, then this requirement can best be expressed by:

a$.4$ X$1+5$ X$2>=8$

b$.(1/4)$ X$1+(1/5)$ X$2<=8$

c$.4$ X$1+5$ X$2<=8$

d$.(1/4)$ X$1+(1/5)$ x$2<=(1/8)$

e$.$ None of the above