Question $20$ is based on the problem and EXCEL spreadsheet below:

Below is the spreadsheet based on the LP model for Cool Dorm Design, Inc. featured in questions $3$ and $4$ above.

$\backslash$table$[[,$A$,$B$,$C$,$D$,$E$],[1,$co$,$Cool Dorm Design,,$],[2,2,x,,cos,10],[3,,$Beds,Desks,,$],[4,$Number to make:,,$1,c,$Total Profit:$],[5,$Unit profit:,$30,40,,],[6,1,$co$,,,],[7,$Constraints:,$4,$L$,$Used,Available$],[8,$Carpentry,$6,4,,36],[9,$Varnishing,$4,8,,40],[10,$Desk demand,$5,1,,8]]$

Using cell references, what EXCEL formula should be entered in cell E$5$ to compute total profit?

a$.=$SUMPRODUCT$($B$4$:B$5,$ C$4$:C$5)$

b$.=$SUMPRODUCT$($B$4$:C$4,$ B$5$:C$5)$

c$.=$SUMPRODUCT$($B$4$:C$4,$ B$8$:C$9)$

d$.$ None of the above