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

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

$G1=$ group replacement labor cost per lamp for $400f{t}^2$ office $-$

$30$ mins

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

$40$ mins

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

Cgroup $400$ft squared Office $=$