Question $4\mathrm{.}0$ Cosine Law: Eh $=(\frac{\text{I}}{d^2}{)}^{**}$Cos$[40pts]$ Applications to Art Museum

In an art museum, $4$ spotlights are used to illuminate the art drawings on walls and sculpture pieces on the floor of its main art gallery.

If $D=0\mathrm{.}78m$ and $S=0\mathrm{.}61m,$ as shown in the figure, the mounting height of the four spotlights is $2\mathrm{.}8m.$ A$.$ Calculate the vertical illuminance $($Ev$)$ of each spotlight with the middle of the art frame at $1\mathrm{.}45$ m $.$ Consider the intensity of each of the spotlight to be $3,140$ Candela. B$.$ What should be the average Lux for art paintings and sculptures in a museum gallery?