A client sells short $500$ shares of SLE $($not eligible for reduced margin$)$ at $\backslash (\backslash$$ $6\backslash )$ a share. Calculate the minimum amount of margin required at the time of sale. a$)\backslash (\backslash$$ $3,000\backslash )$ b$)\backslash (\backslash$$ $1,500\backslash )$ c$)\backslash (\backslash$$ $3,900\backslash )$ d$)\backslash (\backslash$$ $900\backslash )$