$L=$ net price per lamp $-$$$1\mathrm{.}15$

$s=$ labor cost for spot $-$$$\frac{12}{h}r$

G$1=$ group replacement labor cost per lamp for $400f{t}^2$ office $-30$ mi hs

$G2=$ group replacement labor cost per lamp for $600f{t}^2$ office $-40$ mins

$I=$ group re$-$lamping interval $(\%$ of rated lamp life$)-.85$

C Spot$=?$