Writing an IF statement in Excel -

• i have inserted check box (form control) title "wall".
• next have cell stating "false" if unticked , "true" if ticked.
• next 2 cells dimensions of wall "length", "height". - lastly cell containing "area of wall".

i want write if statement in "area of wall" cell when check box ticked, area of wall printed, , if not ticked prints n/a if have written:

 =if((c2="true"), (d2*e2), ("n/a")) 

all happens cell reads n/a, no matter whether box ticked or not. please on how correct this? example

true should not in quotes, it's treating string when it's boolean. removing quotes should work or writing true()

the final formula should this:

=if((c2=true), (d2*e2), ("n/a"))