Example:

 **Cross table**              **Item table**
  Bulk   PKG                    Item  Value
  A        D                      A     2
  A        E                      B     1
  B        F                      C     4
  C        G                      D     5
                                  E     8
                                  F     3
                                  G     1

Item  Value  Bulk  PKG
   A     2
   B     1
   C     4
   D     5      A     D
   E     8      A     E
   F     3      B     F
   G     1      C     G

Item  Value  Bulk  PKG   NEW COLUMN
        A     2                    5
        B     1                    3
        C     4                    1
        D     5      A     D       5.75
        E     8      A     E       9.2
        F     3      B     F       3.45
        G     1      C     G       1.15

New Column = if [Bulk] = null then [Value] else 1.15 * [Value]

New Column = IF( ISBLANK( Table1[Bulk] ), Table1[Value], 1.15 * Table1[Value] )