Duke Carey wrote...
Your statement of the issue is contradictory. If the calculation is
(equity(do you mean debt?)*0.0036/12) when the equity is less than 20%, you'd
simply use

=B7*0.0036/12*B6<.2

Equity usually means the borrower's principal balance, i.e., the sum of
the down payment and principal payments to date.

Your formula above will return TRUE or FALSE, never a numeric result,
because Excel *ALWAYS* gives higher precedence to arithmetic operators
than to comparison operators. In other words, this evaluates the same
as

=(B7*0.0036/12*B6)<.2

while it would appear the OP needs

=B7*0.0036/12*(B6<.2)

Simple Rule: *ALWAYS* parenthesize boolean expressions used as operands
to arithmetic operators.

However, you also mention 15% as some kind of threshold. Is there a
different calculation for equity less than 15%. If so, then....

=IF(B6=0.2,"0",IF(B6=.15,B7*0.0036/12,what's the formula for 0% to 14.9%))
....

If the result should be zero outside the 15% to 20% window, another
alternative would be

=(ABS(B6-0.175)<0.025)*B7*0.0036/12