Using the cut$-$and$-$try method for aggregate operations planning, we can back calculate beginning inventory if we knew the values of other relevant variables. What should have been the in tal invendly an ine el demand, if the production requirement in units of product is $900,$ demand forecast is $1,000,$ and the necessary safety stock is $20$ percent of the demand forecast. Choose the right answer for the bisgining enemie$0$ a$\mathrm{.}300$ b$\mathrm{.}1,9000$ c$.$Cannot find it d$\mathrm{.}100$ e$\mathrm{.}500$