Ok, not that big an amendment required.

Try this array formula**:

=AVERAGE(MMULT(INDEX(C:C,N(IF(1,SMALL(IF(B3:B20={"SALT-in-a-Box sign up","Nexus Survey"},ROW(B3:B20)),{0,1}+2*ROW(INDEX(B:B,1):INDEX(B:B,COUNTIF(B3:B20,"SALT-in-a-Box sign up")))-1)))),{-1;1}))

Obviously you can amend the upper range reference (20 here) as required, though be careful not to make it too large, since every cell referenced will add to the calculation required, whether technically beyond the last-used cells in those ranges or not.

Regards


**Array formulas are not entered in the same way as 'standard' formulas. Instead of pressing just ENTER, you first hold down CTRL and SHIFT, and only then press ENTER. If you've done it correctly, you'll notice Excel puts curly brackets {} around the formula (though do not attempt to manually insert these yourself).