i am trying to create a repeating formula, but use a single cell as a
constant, e.g.

Col A Col B Col C
Row 1 3 3 =(a1*b1)+b4
Row 2 2 3 =(a2*b2)+b4
Row 3 4 2 =(a3*b3)+b4
Row 4 2

in this case b4 is constant in all formulas, while the other variables (a1 &
b1, etc.) naturally adjust when the column is autofilled. My problem is in a
typical autofill, b4 will change to b5 to b6, etc.